Chapter 10 Sexual Reproduction and Genetics

Two of these people are genetically related, can you tell which two?

Section 10.1 - MeiosisMain Idea : Meiosis produces haploid gamates.

Meiosis is a type of cell division that reduces the number of chromosomes.

- 46 pairs reduced to 23 pairs- A cell with half the number of chromosomes

is called haploid. (23 chromosomes n)

This type of cell division is important in the life cycle of organisms such as animals.

Why is meiosis cell division important?Human body cells have 46 chromosomes.

Each parent gives half of their chromosomes (23) to their offspring.

The chromosomes that make up a

pair, one chromosome from each

parent is called a

homologous chromosome.

Passing on genetic traitsEach chromosome

consists of hundreds of

genes.

Genes are DNA

segments that carry

instructions for inherited

traits such as eye color,

hair color, and height

Examples of Inherited TraitsAttached or unattached Can you roll your

earlobes tongue? Some people

can’t.

Hitchhiker thumb

Widow’s peak

How genes are passed from generation to generationOrganisms produce gamete cells (sex cells)

that have half the number of chromosomes as

body cells. (haploid – n chromosomes)

The process of one parent’s gamete combining

with another parent’s gamete is called

fertilization.

Adults have 2n chromosomes

(diploid cells – 46 each)

If diploid cells fertilized each

other, a cell would end up with

92 chromosomes.

The next generation would

have 184 chromosomes.

Eventually there would be too

many chromosomes in each

cell

Instead…Animal cells undergo

meiosis cell division to

reduce the number of

chromosomes before

reproduction occurs.

The offspring receives 23

chromosomes from the

maternal (mother) gamete and

23 chromosomes from the

paternal (father) gamete.

Meiosis involves two consecutive cell divisions called meiosis I and meiosis IIMeiosis I – Reduction Stage

Just like in mitosis, meiosis cell division begins

with Interphase

– cells undergo normal

functions

- DNA replication.

Meiosis I – Prophase IChromatin coils up,

Spindles appear,

Nucleoli disappear,

Synapsis occurs – pairs

of homologous chromosomes form

How is this a little different from

mitosis prophase?

Meiosis I Prophase ICrossing over produces exchange of genetic

information.Crossing over —chromosomal segments are

exchanged between a pair of homologous chromosomes

Meiosis I

Metaphase I

Chromosome centromeres

attach to spindle fibers.

Homologous chromosomes

line up at the equator.

How is this different from

mitosis metaphase?

Meiosis IAnaphase IHomologous chromosomes separate and move to opposite poles of the cell.

Centromere not broken

Chromosome number reduced from 2n to n

How is this different frommitosis anaphase?

Meiosis ITelophase IThe spindles break down.

Chromosomes uncoil and form two nuclei

The cell divides,(cytokinesis).Two daughter cellsare produced with ½ thenumber of chromosomes. (n)

Meiosis II continues the cell divisionTo begin the second set of

meiosis stages, we start

with the daughter cells

from meiosis I.

The DNA will not be

replicated in meiosis II.

If we separate the DNA and divide the cells,

how many cells will be produced?

How many chromosomes in each new cell?

Meiosis II – Prophase II

A second set of phases begins as the spindle

apparatus forms and the chromosomes

condense.

Meiosis II – Metaphase IIA haploid number of chromosomes

line up at the equator.

Meiosis II – Anaphase IIThe sister chromatids are pulled apart at the

centromere by spindle fibers and move toward

the opposite poles of the cell.

Meiosis II – Telophase IIThe chromosomes reach the poles, and the

nuclear membrane and nuclei reform.

Meiosis II - Cytokinesis

Cytokinesis results in four haploid cells, each with n number of chromosomes.

Meiosis I and Meiosis II

Mitosis Meiosis I and II

Males – four sperm made by one cell dividing equally into four.

Mitosis

Meiosis I

Meiosis II

Females – one ovum produced- Unequal division made

during meiosis I and

meiosis II

- Only the large cell

survives and is passed on

- Extra cytoplasm

provides food for the embryo.

The Importance of Meiosis I and II Meiosis consists of two sets of divisions

Produces four haploid daughter cells that are not identical

Results in genetic variation

Meiosis Provides Variation

Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result.

Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine.

Studying a person’s genetic make up

Every person is made

up of trillions of cells,

and each cell carries a

full copy of that person’s

genetic code, in the form

of homologous

chromosomes.

How are these karyotypes different?

Genetic defects – look closely, how are these karyotypes different?

Sexual Reproduction vs. Asexual Reproduction Asexual reproduction = the organism inherits all of its chromosomes from a single parent. The new individual is genetically identical to its parent.Example – binary fission -- involves an equal

division of both the organism cytoplasm and nucleus to form two identical organisms

Asexual ReproductionSpores Vegetative

Propagation

Asexual Reproduction - Regeneration

Body parts that are

missing due to damaged

or predation can be

regrown.

Asexual reproduction - BuddingThe parent plant grows a

structure (a bud) that

matures, falls off and

grows on its own.

Sexual reproduction

Beneficial genes multiply faster over time.

2 parents - combination of genetic material not identical

a) egg and sperm (gametes) combine

fertilization forms zygote

zygote grows by mitosis-creates stem cellsunspecialized cell mass of100 –150 of the first cells toform.

Review of Section 10.1Each student in class has characteristics passed

on to them by their parents.The instructions for the traits are found on

chromosomes in the nucleus.The DNA on the chromosomes is arranged in

segments that control the production of proteinThese DNA segments are called genes.Each chromosome consists of hundreds of genesEach gene has an important role in determining

the characteristics and function of the cell

10.2 Mendelian GeneticsHow Genetics Began The passing of traits to the

next generation is called inheritance, or heredity.

Mendel performed cross-pollination in pea plants.

Mendel followed seven traits in the pea plants he bred.

Examples: flower color, seed color, height of plant, texture of seed.

Self pollenating plant Cross pollinating plant

Mendel’s Experiments – cross-pollination by transferring a male gamete from the flower of one pea plant to the female reproductive organ in a flower of another pea plant.

The Inheritance of TraitsThe parent generation is

also known as the Pgeneration.

Cross two pure parents one yellow & one green

Green trait didn’tdisappear, it was hiddenor masked.

Mendel noticed that some pea plants produce yellow seeds and others produce green.The offspring of this P

cross are called thefirst filial (F1) generation.

= __?__ All yellow

F1 self-pollinates = F2

¾ yellow and ¼ green

Green trait didn’tdisappear, it was hiddenor masked.

Genes in PairsMendel concluded there must be two forms of the seed trait in the pea plants Allele - An alternative form of a single gene

passed from generation to generationThe F1 pea plant had one yellow allele and one

green allele

Dominant – The allele for yellow seed color is dominant over the green seed color (Y)

Recessive – the allele for green seed color is recessive (y)

Law of DominanceAn organism with two of the same alleles for a

particular trait is homozygous

Homozygous yellow –seed plants are YY

Homozygous green-seed plants are yy

An organism with two different alleles for a particular trait is heterozygous.= Yy

When alleles are present in the heterozygous state, the dominant trait will be observed.

Genotype and PhenotypeYou cannot tell an organisms alleles by its

outward appearance. Some traits may be masked.

An organism’s allele pairs

are called its genotype

A yellow plant may have a

genotype of YY or Yy, both

allele pairs will produce

yellow seeds.

Mendel’s Law of SegregationTwo alleles for each trait separate during meiosis.

During fertilization, two alleles for that trait unite.

Heterozygous organisms are called hybrids

Law of Independent Assortment

Random distribution of alleles occurs during gamete formation

Genes on separate chromosomes sort independently during meiosis.

Each allele combination is equally likely to occur.

Genotype and Phenotype

The observable characteristic or outward expression of an allele pair is called the phenotype

The phenotype of pea plants

with the genotype of yy will

be green seeds.

Genotype compared to Phenotype

Predicting Genotypes Punnett Squares and Probability Predict the possible

offspring of a cross between two known genotypes

Each box = 25% chance

Monohybrid Cross

A cross that involves hybrids for a single trait is called a monohybrid cross.

Four boxes in the Punnett square.

Dihybrid Cross is for two traits

The inheritance of two or more traits in the same plant is a dihybrid cross.

Dihybrids are heterozygous for both traits.

Punnett Square—Dihybrid Cross

Four types of alleles (2 traits) from the male gametes and four types of alleles (2 traits) from the female gametes can be produced.

The resulting phenotypic ratio is 9:3:3:1.

Cross Test

Unknown dominant trait

crossed with a known

homozygous recessive,

If offspring show

recessive phenotype,

It is know that the parent

was heterozygous.

10.3 Gene Linkage and PolyploidyGenetic Recombination is

the new combination ofgenes produced bycrossing over andindependent assortment

Sex Chromosomes = One pairFemale = XX andmale = Xy

The X chromosome carries most genes to be passed to offspring.The X chromosome is the

largest, Y being the smallest.

The X chromosome carries genes needed by both males and females

The Y chromosome carries mostly genes for male characteristics.

Co-dominance

Gene Linkage The linkage of genes on a chromosome results

in an exception to Mendel’s law of independent assortment because linked genes usually do not segregate independently.

Incomplete Dominance

Chromosome Mapping Chromosome mapping =

genes in exact locations on

all chromosomes within

organism

farther apart they are more

likely to cross over,

so a higher percentage of

crossed genes would mean

the genes are farther apart

Chromosome map and gene linkage

After the crossover, A and B are together with c, and a and b are together with C on one of the two chromatids of the recombined chromosomes

Polyploidy Polyploidy is the

occurrence of one or more

extra sets of all chromosomes

in an organism A triploid organism, for

instance, would be designated

3n, which means that it has

three complete sets of

chromosomes.

Strawberries are 8n

In humans, polyploidy is lethal, an embryo will not survive.