Lecture 12: Genetics, Epigenetics, and reproduction

What is genetics?

The study of heredity, genes, and genetic variation.

What are chromosomes?

Structures found in pairs (diploid) in body cells and as half pairs (haploid) in gametes.

What are homologous chromosomes?

A pair of chromosomes (one from each parent) that carry the same genes but may have different alleles.

What are sister chromatids?

Identical copies of a single chromosome, connected at the centromere, formed during DNA replication.

What is a karyotype?

A visual representation of an organism’s chromosomes, grouped based on size, shape, and banding patterns.

What is mitosis?

A process where a diploid (2N) mother cell divides to produce two identical diploid daughter cells.

What is the purpose of mitosis?

Ensures genetic consistency for growth, repair, and maintenance.

What type of cells undergo mitosis?

Somatic cells

What is the chromosome number before and after mitosis?

2N → 2N (Mother = Daughter).

What is meiosis?

A type of cell division that reduces chromosome number from diploid (2N) to haploid (N).

What is the purpose of meiosis?

• Produces gametes (sperm and egg cells) for sexual reproduction.

• Introduces genetic variation.h

What type of cells undergo meiosis?

germ cells

What is the chromosome number before and after meiosis?

2N → 1N (Mother ≠ Daughter).

What is a genotype?

• The genetic makeup of an organism (the combination of alleles inherited from parents).

• Example: AA, Aa, or aa.

What is a phenotype?

• The observable physical traits of an organism, determined by genotype and environmental factors.

• Example: eye color, height, coat color in animals.

What is a dominant allele?

• An allele that is expressed if at least one copy is present.

• Example: AA or Aa.

What is a recessive allele?

• An allele that is only expressed if both copies are recessive.

• Example: aa (homozygous recessive).

What is an incross?

• Mating between individuals with identical genotypes (either A/A x A/A or a/a x a/a).

• Used to create inbred strains.

What is an outcross?

• Mating between two genetically different individuals (A/A x a/a).

• Produces heterozygous F1 hybrids.

What is an intercross?

• Mating between two heterozygous individuals (A/a x A/a).

• Used for linkage analysis.

• Produces a mix of genotypes (A/A, A/a, a/a).

What is a backcross?

• Mating an F1 heterozygote (A/a) with a homologous parent (A/A or a/a).

• Used to create congenic strains.

What does the Agouti (A) gene do?

Determines whether hair is yellow (Ay) or is solid-colored (aa) (non-agouti).

What does the Albino (C) gene affect?

• Controls pigment production.

• Mice with homozygous recessive (cc) lack pigment entirely (albino).

What happens with the AyAy genotype in mice?

It is lethal—mice with two copies of the dominant Ay allele do not survive.

What does the Brown Locus (B) control?

Determines whether the pigment is Black or Brown.
B_ = (black)

bb = brown

What does the Dilute Locus (D) affect?

• Controls the intensity of color in the coat.

• The recessive allele (d) dilutes pigment, leading to lighter coat colors.

D_ = normal

dd = dilute (lighter color)

What is epigenetics?

The study of gene expression changes that do not alter the DNA sequence but can turn genes on or off.

How does epigenetics affect coat color in mice?

Genetically identical mice can have different coat colors due to epigenetic modifications.

How can diet influence gene expression?

by modifying epigenetic markers like DNA methylation, affecting coat color and other traits.

Why is epigenetics important in genetics?

It explains how environmental factors can influence traits beyond just genetic inheritance.

How do epigenetic modifications regulate gene expression?

Through mechanisms like DNA methylation and histone modifications, which determine whether genes are active or silent.

Why is epigenetics important for cell differentiation?

It allows embryonic stem cells to develop into different cell types by selectively turning genes on or off.

How do all cells in the body contain the same DNA but perform different functions?

Epigenetic markers regulate gene expression, enabling cells to specialize while sharing the same genome.

What is DNA methylation?

DNA methylation is the addition of methyl (-CH3) groups to DNA (usually at cytosine bases), which silences genes by preventing transcription factors from binding.

How does DNA methylation affect coat color in mice?

increasing Methylation of the Agouti gene in mice leads to darker coat colors.

low DNA methylation allows the gene to remain active.

What are histones and how do they affect gene expression?

proteins that DNA wraps around to form chromatin. Chemical modifications like acetylation or methylation change how tightly DNA is packed, affecting gene activity.

How does histone acetylation affect gene expression?

Histone acetylation loosens chromatin structure, which activates genes by making the DNA more accessible.

Histone acetylation tightens chromatin structure, which silences genes by making the DNA less accessible.

What is the role of non-coding RNA (ncRNA) in gene regulation?

Non-coding RNAs, like microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), regulate gene expression without coding for proteins.

How do miRNAs regulate gene expression?

miRNAs bind to messenger RNA (mRNA) to prevent protein production.

What influence does diet have on DNA methylation levels?

A diet rich in methyl-donors increases DNA methylation levels.

What is imprinting?

Imprinting is an epigenetic mechanism where only one parental allele is expressed.

What mechanisms are involved in imprinting?

DNA methylation and histone modifications.

What can errors in imprinting lead to?

Errors in imprinting can lead to developmental disorders.

What are the main functions of the reproductive system in mammals?

• To produce gametes (germ cells).

• To secrete sex hormones.

What are the main reproductive organs in female mammals?

Paired ovaries and oviducts (fallopian tubes).

What is the function of the uterus?

The uterus or uterine horns are involved in pregnancy and fetal development.

What is the function of the cervix in female mammals?

barrier between the uterus and the vagina, controlling the passage of sperm and menstrual flow.

What are the functions of the vagina, vulva, and clitoris in female mammals?

• The vagina is the birth canal and receives the penis during mating.

• The vulva is the external genitalia.

• The clitoris is an organ of sexual arousal.

What is the function of the testes in male mammals?

The testes produce sperm and secrete male sex hormones (androgens), primarily testosterone.

What is the function of the epididymis in male mammals?

The epididymis is where sperm mature and are stored.

What is the function of the vas deferens (ductus deferens) in male mammals?

transports sperm from the epididymis to the urethra during ejaculation.

What is the function of the urethra in male mammals?

carries sperm from the vas deferens to the outside of the body through the penis.

What is the function of the penis in male mammals?

delivers sperm into the female reproductive tract during mating.

What is the function of the bulbourethral glands in male mammals?

produce pre-ejaculate, which helps to neutralize the acidic environment of the urethra and lubricate the penis.

What is the function of the vesicular glands (seminal vesicles) in male mammals?

secrete fluids that provide nutrients and help with sperm motility.

What is the function of the prostate in male mammals?

secretes fluid that nourishes and protects sperm.

What is the function of the coagulating glands in male rodents?

form a plug to keep sperm inside the female after mating.

What is the genetic sex of females in mammals?

XX chromsomes

What is the genetic sex in males?

XY chromosomes

What determines gonadal sex in mammals?

• XX females develop ovaries.

• XY males develop testes.

What role does the SRY gene play in sex determination in mammals?

The SRY gene on the Y chromosome triggers the development of male gonads. Without this gene, the gonads develop into ovaries.

What is the genetic sex of females in birds?

ZW chromosomes.

What is the genetic sex of males in birds?

ZZ

What chromosome carries the genetic instructions for male development in birds?

The Z chromosome carries the genetic instructions for male development.

What are 0M females in the intra-uterine position phenomenon in mice?

0M females are females surrounded by other females in utero.

What are the behavioral characteristics of 0M females?

• Greater attractivity to males

• Less aggression compared to 2M females

• Less urine marking

What is the estrous cycle pattern of 0M females?

Regular and typical female patterns of estrous cycles.

What are 2M females in the intra-uterine position phenomenon in mice?

2M females are females surrounded by male fetuses in utero.

What are the behavioral characteristics of 2M females?

• Lesser attractivity to males compared to 0M females

• More aggression, likely due to hormonal influences

• More urine marking, typical male-like behavior linked to territorial marking

What is the estrous cycle pattern of 2M females?

Longer and more irregular estrous cycles compared to 0M females.