BEYOND MENDELIAN

GENETICS AND HUMAN

GENETICSFreshman Biology

Semester Two

PATTERNS OF INHERITANCE Autosomal Dominant/Recessive

Gene for Trait is found on a autosomeCan be dominant or recessive

Sex-linkedGene for Trait is found on a sex

chromosomeMost (almost all) are found on X (many

more genes than Y)Can be dominant or recessive

INHERITANCE OF SEX Moms give

Sons and Daughters one of their X chromosomes (random choice)

Eggs have a single X chromosome Dads give

Daughters their X chromosomeSons their Y chromosomeHalf of the sperm carry an XHalf carry a Y

X-LINKED TRAITS Moms

No “bad” X’s- 0% chance of passing onOne “bad” X- have a 50% of passing the

“bad” X to their offspringTwo “bad” X’s- have a 100% chance of

passing one of them on Dads (can only have one copy)

Only pass the “bad” X to daughters; sons get the Y

X-LINKED PUNNETT SQUARE Genotypes of each parent are written as

superscripts on their sex chromosomesEx: XHXh and XhY

Remember males only have one copy because they only have one X

DO NOT CROSS TWO FEMALES When analyzing data

If question asks about offspring, consider all 4

If question narrows it down to one sex, only look at the two of that sex

Y-LINKED TRAITS Only Males can have them Dads pass on the trait to all sons

X-LINKED PUNNETT SQUARE

RECESSIVE X-LINKED DISORDERS Show up more in males

Females have two X’s Harder to inherit two “bad” X’s to show disorder

Males have only one Easier to inherit the one copy needed for them

to show the disorder

BEYOND MENDEL Incomplete dominance Codominance Multiple alleles Polygenic traits Multifactorial traits

INCOMPLETE DOMINANCE One allele is not completely dominant

over the other; heterozygotes show a blending of the trait

CODOMINANCE Neither allele is

dominant over the other; heterozygotes express both alleles at the same time (not a blending)

Ex: Both black and white feathers in chickens

Ex: Both white and red hairs in roan cattle

REVIEW – INC. & CODOMINANCE In tulips, yellow

color is incompletely dominant to red. Cross a homozygous yellow tulip with a homozygous red tulip. Determine genotypic and phenotypic ratios of the offspring.

A purple-feathered penguin (P) mates with a green penguin (G). What are the

genotypes and phenotypes of their offspring?

If two of the above offspring mate, what is the phenotypic ratio of their offspring?

MULTIPLE ALLELES Gene has more than just two alleles

possible Remember- each individual still just has

2 Ex- rabbit fur color (4 alleles)

HUMAN BLOOD TYPES Human Blood Types have a gene that

displays multiple alleles and codominance

ABO gene has three alleles IA codes for a A-type ID tag on red blood

cells IB codes for a B-type ID tag on red blood

cells i codes for no ID tag on red blood cells

IA and IB alleles are codominant

HUMAN BLOOD TYPES CONTINUED Possible Phenotypes and Genotypes

A blood type (IAIA or IAi)B blood type (IBIB or IBi)AB blood type (IAIB)O blood type (ii)

POLYGENIC TRAITS More than one gene codes for a trait Wide range of phenotypes and

genotypes possible Ex- eye color

MULTIFACTORIAL TRAITS Phenotype is a blend between

genetic inheritance and environment

REVISITING INDEPENDENT ASSORTMENT Not all genes independently assort Only happens with genes on

different chromosomes Genes on the same chromosome are

linked (where one goes the others go too) For example, if

One homologous chromosome has alleles A, B, and c for three genes

The other homologous chromosome has alleles A, b, and C

Then the offspring cannot get A, B, and C or a, b, and c or any other combinations

CROSSING OVER REVISITED Crossing-over can change the

combinations of linked genes The further apart that two genes are

on a chromosome, the more likely that they are to cross-over

Gene maps are maps of chromosomes that show the locations of genes and the distances between them

HUMAN GENETICS Humans have 23 paired

chromosomes in somatic cells Each chromosome has many genes

located on it Some genes have a simple

Mendelian type of inheritance Most traits have a complex

inheritance Polygenic traitsMultiple Alleles Influenced by Both Genetics and

Environment

KARYOTYPES A karyotype is a diagram of

chromosomes within a cell Homologous chromosomes are

paired Autosomes (non-sex chromosomes)

are arranged from largest to smallestLargest autosome is #1: smallest

autosome is #22 Sex chromosomes are last (#23)

XX in femalesXY in males

KARYOTYPE INFO Karyotypes can tell:

Sex of IndividualPresence of a Chromosomal Disorder

Extra or missing whole chromosomes Large extra or missing piece of chromosome

Can’t tell:Genetic Disorders from Small Mutations

CHROMOSOMAL ABNORMALITIES Missing or extra whole

chromosomes or pieces of chromosomes

The condition is determined by which chromosome is affectedThis is because each chromosome has

different genes May affect all cells

Fertilized egg had the mistake Person may be a mosaic (some

normal, some bad)Mistake happened later in development

NONDISJUNCTION Mistake during Meiosis or Mitosis Non-disjunction: failure of the

chromosomes to separate properlyOften happens in Anaphase I when tetrads

separate

TERMS FOR CHROMOSOMAL DISORDERS Trisomy

3 copies of one type of chromosome Monosomy

1 copy of one type of chromosomeOnly monosomy that is viable is XO

SPECIFIC DISORDERS Down’s Syndrome (Trisomy 21)

Edwards Syndrome (Trisomy 18) Characteristics

Patau Syndrome (Trisomy 13)

Turners Syndrome (XO)

Kleinfelter Syndrome (XXY)

DOWN SYNDROME (CHARACTERISTICS)

PATAU SYNDROME (CHARACTERISTICS)

TURNER SYNDROME (CHARACTERISTICS)

KLINEFELTER SYNDROME (CHARACTERISTICS)