Lecture 11 Flashcards
What are somatic cells
All cells that are not sperm or egg)
Gametes contain how much of the genetic material necessary to form a complete organism
Half
What type of cell are gametes
Haploid
What do testes consist of
Highly coiled tubes called seminiferous tubules
Where are sperm cells produced
In particular cells found in seminiferous tubules
What secretes sex hormones (male)
Testes
What do the ovaries produce
Eggs, female sex hormones, estrogen, progesterone
Pathway of egg
- Released from ovary (ovulation)
- Fimbriae of uterine tube catches it
- Cilia in uterine tube moves it down to uterus
- Egg exits uterus via cervix
- Opening in cervix leads it to vagina
Where does fertilization occur
Uterine tube
Which organs are both in reproductive and endocrine system
Ovaries and testes
How are sex cells produced
Meiosis
Meiosis produces cells that
- Have half # of chromosomes of parent cell
- Genetically different
Why gametes have only 23 chromosomes
Bc when female + male combine = 46 chromosomes (normal cell, or else 92)
Which chromosomes come from mom/dad
Dad : X or Y
mom : X
What are all the cells except sex cells called
Autosomes
(We have 22 pairs of autosomes)
What is a homologous pair
When two chromosomes have same genes (ex: pair #1 of karyotype)
Homologous chromosomes have
Same genes but may have different alleles
What are alleles
Alternative versions of genes (ex same gene but one codes for blue eyes and other brown)
Job of meiosis
Convert diploid cells in ovaries or testes into haploid sex cells
How many daughter cells in meiosis
After meiosis I : 2 daughter cells
After meiosis II : 4 daughter cells
In prophase I :
Same as mitosis, but HOMOLOGOUS PAIRS LINE UP
What is crossing over
Paired homologous chromosomes exchange genetic material between nonsister chromatids
Result of crossing over
Chromosomes will have same # genes but sister chromatids are no longer identical
Metaphase I :
PAIRS of homologous cell line up at metaphase plate
Anaphase I :
Homologous pairs separate but chromatids remain attached
Result of anaphase I
Bc homologous pair separate, ends of cell have 1 set of chromosomes meaning: diploid -> haploid
Telophase I
Chromatids still attached, nuclear membrane reappears
Cytokinesis I
Daughter cells have both copies of ONE kind of chromosome, haploid and genetically diff from each other
Overall of meiosis I
Crossing over and separation of homologous chromosomes,
Goal of meiosis II
Separate sister chromatids
Prophase II
Nuclear membrane disappears, spindles attach to kinetochore, centrosomes disappear
Metaphase II
Chromosomes line up in middle ( sister chromatids are diff bc of crossing over)
Anaphase II
Sister chromatids separate
Telophase II
Nuclear membrane forms, haploid set of chromosomes on each side of the
Cytokinesis of meiosis II
Each cell divides into total of 4, each have single copy of chromosomes
What is the original source of genetic diversity
Mutations
Mutations create diff versions of genes called
Alleles
Reshuffling of alleles during sexual reproduction produces
New combinations of genes and increases genetic variation
Behaviour of chromosomes during meiosis/fertilization is responsible for
Most of genetic variation
Three mechanisms contributing to genetic variation
- Independent assortment of chromosomes(meiosis)
- Crossing over (meiosis)
- Random fertilization
In meiosis I, homologous pairs orient how?
Randomly
Crossing over produces what type of chromosomes
Recombinant (combine genes inherited from both parents)
Where can crossing over occur in a chromosome
Anywhere
The fusion of two gametes produces
A zygote with about 70 trillion diploid combinations
What is nondisjunction
Failure of chromosomes to separate during meiosis
What arise as a result of abnormal meiotic division
Aneuploidies
Nondisjunction can occur in both…
Autosomes and sex chromosomes
Down syndrome/trisomy 21/autosomal aneuploidy has how many chromosomes
47 (1 extra chromosomes 21)
Down syndrome characteristics
Highest rate of occurrence of genetic disorders
More from maternal distinctions
Genes on chromosomes 21 over-expressed
Edward’s syndrome (extra chr 18)
-affect all systems of body
-about 95% of fetuses die before birth
-infants have 5% chance to survive to age 1
Patau syndrome (extra chr 13)
85% of 15% survivors past one month dot survive past 1yo
Most fetuses die before birth
Single X chr (lack of Y) makes
Females with Turner’s syndrome
(Less developed breast/ovaries, no puberty)
Single Y chr with 2 or more X chr makes
Males (bc Y chr) with Klienfelter syndrome (feminine features, less developed testes)
Is the Y or X chr required in humans
X chromosome
One X chr is inactivated in humans so the extra X is
A barr body (dense metabolically inactive X chr)
Barr bodies explain why extra X chr is not severe compared to extra autosome as it
Turns “off”
