Biology Genetics/hormones etc. DP1

Menstrual cycle & hormones, genetic expression ...

Phenotype

An observable trait determined by genotype and environmental factors

Genotype

The combination of alleles inherited by offspring

Discrete variation

Defined by categories, not in a scale. Controlled by a single gene, the environment has no effect (yes/no to having the phenotype)

Continuous variation

Controlled by multiple genes - polygenic. There is an environmental influence and a very broad range, no distinct categories

What occurs in the follicular phase

Day 1-14

FSH causes a ring of cells around the egg (follicle) to develop

As the follicle develops, it secretes estrogen

As estrogen increases, so does FSH, causing follicle to develop more and secrete more estrogen, causing more FSH, etc.

At high levels of estrogen, it inhibits FSH and triggers LH

The surge of LH causes the egg to rupture from the follicle and leave the ovary to the fallopian tubes
The follicle remains in the ovary with no egg

What occurs at ovulation

The surge of LH causes the egg to rupture from the follicle and leave the ovary to the fallopian tubes

What does the follicle secrete as it develops

Estrogen

Positive feedback loop hormones

FSH and estrogen in follicular phase

Role of estrogen in the menstrual cycle

Thickens endometrium lining and triggers LH

Role of FSH in the menstrual cycle

To grow the follicle (the ring of cells) around the egg, the egg can mature into an oocyte

What occurs in the luteal phase

The remaining follicular cells w/ no egg are now corpus luteum

Corpus luteum secretes estrogen & progesterone

Progesterone levels rise as days go by and thicken the endometrium

Progesterone inhibits FSH and LH (as no new egg needs to be released)

If pregnancy does not follow, corpus luteum breaks down

This causes a drop in progesterone since nothing is secreting it, so nothing can keep up the endometrium lining and it is shed as menstruation

Since little progesterone is there, nothing is inhibiting LH and FSH, so the cycle starts again

Role of progesterone in the menstrual cycle

Thickens the endometrium, which is required for embryo implantation as it will provide embryo nutrients etc. for growth and inhibits FSH and LH.

Negative feedback loop in menstrual cycle

Progesterone inhibiting FSH & LH

Steps of IVF

Injections given to stop FSH & LH (doctors need to control cycle)

High levels of FSH injected to start superovulation, where many follicles are developed and many eggs are released

The eggs are harvested from the follicles

Fertilization occurs outside of body (eg. in petri dish)

Fertilized eggs implanted back into uterus along with progesterone injections to keep the endometrium lining sufficient for embryo

Autosomal disease

An inherited disease occurring on non-sex chromosomes (any other of the 22 pairs).

PKU

Recessive autosomal disease: must have 2 recessive alleles to show, one to carry
A mutation in the PAH gene that codes for phenylalanine hydroxylase) needed to convert phenylalanine to tyrosine. This leads to a build up of phenylalanine, which can impair brain development.

Cystic Fibrosis

Recessive autosomal disease: must have 2 recessive alleles to show, one to carry
A mutated CFTR protein is unable to regulate movement of salt in & out of cells, leading to a sticky, thick mucus that clogs the lungs and makes it hard to breathe

Sickle cell disease

Recessive autosomal disease: must have 2 recessive alleles to show, one to carry
Single point mutation in the HBB gene on chromosome II, leading to haemoglobin S being mutated, red blood cells are cresent shaped, rigid, and sticky = they can clump together and restrict blood flow

How does a pregnancy test work

The test detects hCG, which the embryo secretes when implanted into the uterus. When you pee on the stick, the antibodies from the stick bind to hCG, triggering a reaction and activating a dye.

Homologous chromosome

Same genes in the same locations

Not always the same alleles

Independent assortment

Occurs in metaphase: the chances of the mother chromosome facing a pole and the father chromosome facing another are completely random and independent of each other, so when they get pulled away, the probability of a certain chromosome being located on a certain side is random.