Beyond mendelian genetics and human genetics Freshman Biology Semester Two

Patterns of inheritance Autosomal Dominant/Recessive Gene for Trait is found on a autosome Can be dominant or recessive Sex-linked Gene for Trait is found on a sex chromosome Most (almost all) are found on X (many more genes than Y)

Inheritance of sex Moms give Dads give Sons and Daughters one of their X chromosomes (random choice) Eggs have a single X chromosome Dads give Daughters their X chromosome Sons their Y chromosome Half of the sperm carry an X Half carry a Y

X-linked traits Moms Dads (can only have one copy) No “bad” X’s- 0% chance of passing on One “bad” X- have a 50% of passing the “bad” X to their offspring Two “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 chromosomes Ex: 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 traits Multiple 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 smallest Largest autosome is #1: smallest autosome is #22 Sex chromosomes are last (#23) XX in females XY in males

Karyotype info Karyotypes can tell: Can’t tell: Sex of Individual Presence 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 affected This 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 properly Often 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 chromosome Only 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)