1. Beyond mendelian genetics and human genetics
Freshman Biology
Semester Two

2. 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)

3. 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

4. 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

5. 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

6. Y-linked traits Only Males can have them
Dads pass on the trait to all sons

7. X-linked punnett square

8. 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

9. Beyond Mendel Incomplete dominance Codominance Multiple alleles
Polygenic traits
Multifactorial traits

10. Incomplete dominance
One allele is not completely dominant over the other; heterozygotes show a blending of the trait

11. 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

12. 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?

13. Multiple alleles Gene has more than just two alleles possible
Remember- each individual still just has 2
Ex- rabbit fur color (4 alleles)

14. 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

15. 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)

16. Polygenic traits More than one gene codes for a trait
Wide range of phenotypes and genotypes possible
Ex- eye color

17. Multifactorial traits
Phenotype is a blend between genetic inheritance and environment

18. 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

19. 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

21. 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

22. 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

24. 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

25. 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

26. nondisjunction Mistake during Meiosis or Mitosis
Non-disjunction: failure of the chromosomes to separate properly
Often happens in Anaphase I when tetrads separate

27. 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

28. Specific disorders Down’s Syndrome (Trisomy 21)
Edwards Syndrome (Trisomy 18)
Characteristics
Patau Syndrome (Trisomy 13)
Turners Syndrome (XO)
Kleinfelter Syndrome (XXY)

29. Down syndrome (Characteristics)

30. Patau syndrome (Characteristics)

31. Turner syndrome (characteristics)

32. Klinefelter syndrome (characteristics)