the transmission of traits from one generation to the next

- whicle offspring look similar to parents, they are not identical clones

having two sets of chromosomes, one form each parent

• chromosome 23
• deal with sex/ gender

1. bring diploid cells down to haploid
2. increase genetic diversity

• "Equational Division" 
• start and end with same number of chromosomes
• in humans, in somatic diploid cell starts with 46 and ends with 46 chromosomes

"Reduction Division"

• end with half number of chromosomes as started
• start with 46 chromosomes and end with 23 chromosomes
• have separated the homologous pairs

• special phase that leads to genetic diversity
• Crossing Over

What is crossing Over

• Homologous pairs of chromosomes line up and parts of the chromosome (one from mother and one from father) are switched

via Homologous Recombination

- genetic recombination where nucleotide sequences are exchanged between two identical, DNA molecules

-Crossing over happens ONLY between HOMOLOGOUS CHROMOSOMES

What happens in metaphase I

• chromosomes line up at the equator of the cell
• Independent Assortment
• another genetic diversity

arrangement of chromosome at the middle is random

- so each daughter cell has a mixture of chromosomes from the mother or the father, not uniform

• the chromosomes are pulled to seperate ends of the cell
• GOES FROM DIPLOID DOWN TO HAPLOID

chromosomes reach the poles

- then cells go straight into Meiosis II

• sister chromatids are what seperate

• either Meiosis I or II

• it is more sever if it occurs in Meiosis I- if homologous pair fails to sperate that means that all progeny cells, and all of the gametes are abnormal in chromosome number

• then only half the gametes produced have an abnormal chromosome number

incorrect chromosome number

- almost never tolerated in larger chromosomes and is almost fatal to fetus or shortly after birth

-in smaller chromosomes it is a little more tolerated

• nondisjunction occurred with chromosome 21
• most common serious birth defect- affect 1 in 700 children

How are children with down syndrome characterized

• flat face, wide almond eyes, flattened nose, small head, and short neck
• mild to moderate intellectual impairment
• physical abnormalities such as heart defects and immune disorders

• happens when females only have 1 X chromosome  instead of 2

What are characteristics of Turner Syndrome

• no mental impairment
• short stature, broad chest, low hairline, webbing of the neck
• infertile

• Do not suffer cognitive impairment
• the men have rather feminine symptoms
  • less muscle mass
  • less body hair
  • broader hips, smaller genitalis
  • fat deposited around hips and stomach
• typically, sterile and do produce children successfully