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Genetics
Genetics is the scientific study of heredity and variation.
GeneticsIn asexual reproduction:•Single-celled organisms reproduce by simple cell division •There is no fertilization of an egg by a sperm
Asexual ReproductionFUNCTIONS OF CELL DIVISION
Sea stars
LM
Amoeba African Violet
Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis.
Genetics
Genetics
Gregor Mendel•Worked in the 1860s•Was the first person to analyze patterns of inheritance•Deduced the fundamental principles of genetics
GeneticsRemovedstamensfrom purpleflower.
White
Stamens
Purple
Transferred pollen fromstamens of white flowerto carpel of purpleflower.
Parents(P)
Carpel
Offspring
(F1)
Pollinated carpelmatured into pod.
Planted seedsfrom pod.
Mendel studied garden peas because they:
•Easy to grow
• Come in many readily distinguishable varieties
• Easily manipulated
• Can self-fertilize
Genetics• A character is a heritable
feature that varies among individuals.
• A trait is a variant of a character.
• Each of the characters Mendel studied occurred in two distinct forms.
*P - parental generation*F1 – first filial generation*F2 – second filial generation
-Example:
X
Tall Dwarf
P
F1 – all Tall
Tall
F2
Genetics
Mendel’s hypotheses (to explain his results)
*genes and alleles
1. Alternative versions of genes (alleles) account for variation in inherited characters.
2. For each character, an organism inherits two alleles, one from each parent.
Genetics
3. If two alleles differ, one is dominant, the other recessive
X
Tall Dwarf
P:
DD dd
F1 – all Tall
TallDd
4. The two alleles for each character segregate (separate) during gamete production.
Mendel’s Law of Segregation
Genetics
GeneticsA Punnett Square predicts the results of a genetic cross between individuals of known genotype
D d d
Tall DwarfP: DD ddX
Gamete formation: D
*genotype
*phenotype
*Homozygous
*Heterozygous
D
D
d d
D d D d
D d D d
4/4 are Dd
4/4 are Tall
Genetics
Dihybrid cross- A genetic cross between two individuals involving two characters
GGWW ggww
Example:
P1
yellow, round
green, wrinkled
XGW GW GW GW
gw
gw
gw
gw
GgWw
Genetics
F1
All yellow, round
F1
All yellow, roundGgWw
F1
All yellow, roundGgWw
X
F2
9/16 yellow, round
3/16 yellow, wrinkled
3/16 green, round
1/16 green, wrinkled
GW Gw gW gw
gW
GW
gw
Gw
9:3:3:1 Phenotypic ratio; Genotypic ratio as follows:
1/16 GGWW, 2/16 GGWw, 2/16 GgWW, 4/16 GgWw1/16 GGww, 2/16 Ggww
1/16 ggWw, 2/16 ggWw
1/16 ggww
Mendelian inheritance is based on probabilityExample- coin toss
*1/2 chance landing heads
*Each toss is an independent event
*Coin toss, just like the distribution of alleles into gametes
*The rule of multiplication – determines the chance that two or more independent events will occur together
½ x ½ = ¼
B
B
b
Bb
b
Fem
ale
gam
etes B B
B
b b b
Male gametes
Formation of sperm
Bb male
Formation of eggs
Bb female
F2 Genotypes
F1 Genotypes
( )
12
14
12
12
12
14
14
14 1
212
Genetics
Female MaleAttachedFree
Third generation(brother and sister)
Second generation(parents, aunts, and uncles)
First generation(grandparents) Ff Ff
FfFF ff fforFf
ff FForFf
Ffff
Ff ff
Genetics: Pedigrees
Human Disorders