Non-Mendelian Genetics

Mendelian Genetics

•Complete dominance

• Law of segregation

• Law of independent assortment

•One gene one trait

Non-mendelian Genetics

• Codominance

• Incomplete dominance

• Multiple alleles

• Sex-related inheritance

• Polygenic inheritance

• Pleiotropy

• Epistasis

Codominance

- two dominant alleles affect phenotype in separate ways

- both alleles manifest

- e.g. roan coloring in horses – both red and white

Incomplete dominance

- phenotype of offspring is between phenotypes of two parents

- e.g. red and white parents give rise to pink offspring

Multiple alleles

- genes with more than two alleles that control the phenotype

- e.g. ABO blood type system has 3 alleles--IA,IB,i. IA,IB are codominant, i is recessive to both

Non-mendelian inheritance (1st Law) Alleles with different degrees of dominance and recessiveness

Sex-related inheritance expression of traits is affected by the sex of the individual

• sex is an inherited phenotypic character determined by the presence/absence of certain chromosomes

• SRY (sex-determining region of Y) in humans

1. Sex-linked inheritance

2. Sex-limited inheritance

3. Sex-influenced inheritance

Sex-linked inheritance

• Gene linkage – genes located on the same chromosome are inherited together

• Sex-linkage

• Sex chromosomes contain genes for many characters unrelated to sex

• X-linked/Y-linked gene

http://news.sciencemag.org/biology/2014/04/y-chromosome-more-sex-switch , http://ghr.nlm.nih.gov

So much more than just sex chromosomes

Y chromosome

• 50-60 genes

• e.g. SRY, USP9Y

X chromosome

• 800-900 genes

• wide range of functions not related to sex

Examples of X-linked traits

Recessive alleles

• Color-blindness

• Duchenne muscular dystrophy

• Hemophilia

• Testicular feminization

Dominant traits

• Hypophosphatemia

Checkpoint 1

A

If a mother was a carrier for the recessive sex-linked gene for defective color vision and the father was normal, would their sons or daughters have defective color vision?

B

If a father and his son both have defective color vision, is it likely that the son inherited the trait from his father?

Examples of Y-linked (Holandric) Inheritance

Transmission of genes from father to son

• Testis-determining factor (TDF/SRY gene)

• Hypertrichosis of the ears

Checkpoint 2

Hypertrichosis of the ear is a Y-linked trait, a woman is married to an affected man. Is it possible for her to have:

a) An affected son?

b) An affected daughter?

c) An affected granddaughter by her daughter?

d) An affected grandson by her daughter?

1. Autosomal dominant

2. Autosomal recessive

3. X-linked dominant

4. X-linked recessive

5. Y-linked

Using pedigrees to detect inheritance patterns

a. Y-linked? b. Dominant or recessive? c. Autosomal or X-linked? d. What is the genotype of individual I-1? e. I-1 and I-2 have another child. What are the chances that their child will be an affected boy?

Affected males have sons who are also affected

Females are not affected

Checkpoint 3

Appears every generation Males and females equally

affected Affected offspring has at

least one affected parent Affected parents may have

unaffected offspring

Checkpoint 4

a. Y-linked? b. Dominant or recessive? c. Autosomal or X-linked? d. What is the genotype of individual I-1? e. I-1 and I-2 have another child. What are the chances that their child will be an affected boy?

Can skip a generation Males and females equally affected Affected parents only have

affected offspring Affected offspring may have

unaffected parents

Checkpoint 5

a. Y-linked? b. Dominant or recessive? c. Autosomal or X-linked? d. What is the genotype of individual I-1? e. I-1 and I-2 have another child. What are the chances that their child will be an affected boy?

Present every generation More affected females than males Affected mother ½ to all

offspring are affected Affected father all daughters

are affected

Checkpoint 6

a. Y-linked? b. Dominant or recessive? c. Autosomal or X-linked? d. What is the genotype of individual I-1? e. I-1 and I-2 have another child. What are the chances that their child will be an affected boy?

Can skip a generation Unaffected parents may have affected

offspring More affected males than females Affected mother all of sons are affected Affected father all daughters are carriers

of the trait

Checkpoint 7

a. Y-linked? b. Dominant or recessive? c. Autosomal or X-linked? d. What is the genotype of individual I-1? e. I-1 and I-2 have another child. What are the chances that their child will be an affected boy?

Sex-limited inheritance

• involves autosomal genes that are expressed only in either males or females

• resulting in a part or function of the body that is present in one sex but not the other

• Examples: • milk production

• cryptorchidism

• feathers in domestic fowl

Genotype Female Male

HH hen-feathered hen-feathered

Hh hen-feathered hen-feathered

hh hen-feathered rooster-feathered

Checkpoint 8

Rooster feathering in chickens is a trait limited in expression only in males and determined by the autosomal recessive genotype hh. The dominant allele (H) produces hen-feathered males. All females are hen-feathered regardless of genotype.

A rooster-feathered male mated to a female produces 12 chicks: 6 hen-feathered females, 3 rooster-feathered males and 3 hen-feathered males. What is the genotype of the female parent?

Genotype Female Male

HH hen-feathered hen-feathered

Hh hen-feathered hen-feathered

hh hen-feathered rooster-feathered

Sex-influenced inheritance

• dominant in one sex but recessive in the other

• autosomal

• difference in expression due to the hormonal difference between the sexes • in heterozygotes, the expression of the trait is

affected by sex hormones

• homozygotes are unaffected and express the trait regardless of the hormone produced

Sex-influenced inheritance

•pattern baldness •baldness allele is

dominant in males but recessive in females

• a heterozygous male is bald, but a heterozygous female is not

Genotype Female

recessive

Male

dominant

b1b1 bald bald

b1b2 not bald bald

b2b2 not bald not bald

Checkpoint 9

Pattern baldness is a sex-influenced trait that is dominant in men and recessive in women. A

heterozygous bald man marries a bald woman. What are the phenotypic expectations for their children and their corresponding probabilities?

Genotype Female

recessive

Male

dominant

b1b1 bald bald

b1b2 not bald bald

b2b2 not bald not bald

Reminders

1. Bio – First Periodic Exam on Nov 26, Th

2. PostQuarter for the following people will be at SHB111

at 1030AM, after the Math Periodic Exam

• Truth – Capule, Opulencia

• Photon – Tiamson, Navarra

• Graviton – Ang, Buenviaje, De Velez, Kim, Abulencia, Almonte, Gascon

3. Portfolio (5%) of grade and End of Quarter Reflection

questions due on Dec 7, Monday – on second quarter

topics only

4. Notebooks for those with grades lower than 1.75,

resubmissions, etc. are due on Nov 26, Th, 11AM at

SHB109