Genetics Exam 2 2/5 - Sex Linked Inheritance

Haplodiploidy definition

Grasshopper:

Diploid female XX

Haploid male XO

Homogametic Male meaning and combination

ZW: female

ZZ: male

Factors that can affect gender

Temperature, location, social

What does it mean that the X chromosome “acts as a homolog” to the Y chromosome in males?

• Males have one X chromosome and one Y chromosome

• X and Y are not fully homologous (different size & genes)

• They share small identical regions:

  • Pseudoautosomal regions (PARs)

• In PARs, X and Y:

  • Pair during meiosis

    • Segregate properly

What are the key characteristics of the Y chromosome?

• Smaller than the X chromosome

• Contains ~ 231 genes

• Carries genes important for male development (e.g., SRY)

• Has many palindromic DNA sequences

  • Can form loops → disrupt replication

  • ↑ risk of mutations / deletions

• Only partially homologous with X:

  • Matches at pseudoautosomal regions (PARs)

  • Allows pairing during meiosis

where can we find Pseudoautosomal regions (PAR1 and PAR2)?

Y chromosome

5% of chromosome, contains genes shared with X chromosome

where can we find male specific region? MSY

Y chromosome

95% of Y

contains SRY (sex determining region) and AZF (for sperm production)

What is a transcription factor?

Controls the expression of other genes

• Activate gene transcription (turn genes ON)

• Repress gene transcription (turn genes OFF)

Chromosomal / Genetic meaning

XX or XY

Gonadal meaning

Differentiation of gonads

Phenotypic meaning

Expression of other sex characteristic

gender meaning

Psychosocial aspect of being a man or woman. (social, expectation…)

Gender Identity

Feelings of being a man or woman.

Sexual Orientation

Attraction to same and/or opposite sex.

What does hemizygous mean?

• Having only one copy of a gene instead of two

• Occurs when there is no homologous allele present

Example:

• Males (XY) are hemizygous for X-linked genes

  • Only one X chromosome

  • No matching gene on Y chromosome

👉 Any allele present is expressed (no second copy to mask it)

Trait only affects only male or only female bodies.

sex limiting traits

can be autosomal or allosomal (sex chromosome)

Allele is dominant in one sex but recessive in another

Sex Influenced

maybe due to difference in hormone levels

baldness Bb in men completely bald

baldness bb in women still have some hair

What is X-inactivation?

One X chromosome in each cell is turned OFF (inactivated)

What is a Barr body?

Barr body = inactive X chromosome

• It becomes tightly packed (condensed DNA) - silenced” X chromosome

What is X-inactivation skewing?

one X is turned off more often than the other (paternal or maternal)

Different types of X-inactivation of skewing?

Primary skewing (genetic)

• Some X chromosomes are “preferred” for inactivation

• Controlled partly by genes like Xce

Secondary skewing (more common)

• Happens later due to selection

• Example:

  • if one X carries a harmful mutation

  • cells using it may die off

    • leaving more cells using the other X

what does it mean X-inactivation affects heterozygous loci in XX females

Even though a female has two different alleles,
➡ each cell only expresses one of them

So the body becomes a patchwork of expression.

What is Somatic Cell Nuclear Transfer (SCNT) and what is it for?

For cloning

• Take the nucleus from a somatic (body) cell

• Insert it into an egg cell with its nucleus removed

• Stimulate it to develop into an embryo

  • Implant into a surrogate → develops into a clone

How do you identify inheritance pattern?

You cannot directly prove it, can only eliminate patterns

• Y-linked: only males are affected

• Dominant (all generations) or Recessive (can skip generations)

• X-Linked or Autosomal (happens equally in male and female