Meiosis & Chromosomes Chapter 10.1 and 11.3

Chromosome Structure DNA coils around histones (proteins) to form nucleosomes, This coils to form chromatin fibers. The chromatin fibers supercoil to form chromosomes that are visible in the metaphase stage of mitosis. https://www.youtube.com/watch?v=tsVHWbXqum8&t=249s

How many chromosomes do we have in our cells? Human body cells have 46 chromosomes Each parent contributes 23 chromosomes Homologous chromosomes - a pair of chromosomes that have the same genes

Homologous Chromosomes -Same length -Same centromere position (middle) -One maternal and one paternal chromosome

Homologous Chromosomes Carry the same genes that control the same inherited traits Alleles are the variations of one gene Ex: eye colors can brown, blue, green, hazel, etc…. You inherit one chromosome from each parent!

DO NOW Label the following structures:

Pairs #1-23 23 pairs = 46 total chromosomes These are your chromosomes! 1 chromosome in each pair comes from your mother and father!

Unduplicated homologous chromosomes Duplicated homologous chromosomes

Karyotyping A micrograph that shows pairs of homologous chromosomes in decreasing size 46 chromosomes, 23 pairs Pairs #1 - 22 are autosomes Pair #23 are the sex chromosomes XX or XY

Karyotype

Chromosomal Mutations - nondisjunction Monosomy – Results in a sex cell with one less chromosome Trisomy – Results in a sex chromosome with one extra chromosome Chromosomal Mutations - nondisjunction

Do Now 1. How many autosomes? 2. How many sex chromosomes? 3. What is the sex of this patient? 4. Monosomy, Trisomy? 5. Is this individual normal?

Before we start genetics, let's review the process of what makes us all look different compared to our siblings, family, and classmates!

Sexual Reproduction Sexual reproduction creates genetic variability. That is why we all look different and you look different from your siblings!

Define the following words… Meiosis: Sexual reproduction-production of gametes Gamete: Sex Cells (egg = females & sperm = males) contain half the number of chromosomes (23) Somatic Cells: Body Cells Contain 46 chromsomes

Haploid: Half the chromosome number (n) 1 of each pair of chromosomes (23) Gametes are haploid Diploid: 2 of each type of chromosome (2n) Somatic cells are diploid Fertilization: Sperm enters egg Zygote: Fertilized egg (diploid)

Can you apply terms learned on the past few slides to this picture? Think - Pair - Share Can you apply terms learned on the past few slides to this picture?

Meiosis The sexual life cycle in animals involves meiosis Meiosis produces gametes (23 chromosomes). When gametes combine in fertilization, that creates a zygote. A zygote has 46 chromosomes

Meiosis 2 Divisions Meiosis I - separation of homologous chromosomes Meiosis II - separation of sister chromatids

DNA Replication before Meiosis 1 Before Meiosis begins, all DNA must be replicated

Meiosis 1 Crossing over occurs Homologous chromosomes separate, randomly! 46 Duplicated 23 duplicated Crossing over = the exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring.

Crossing over The same genes “switch”, which allows for unique gametes to form, different from the exact chromosomes given from the mother and father. Occurs during Meiosis 1, Prophase 1

Each gamete has a unique combination of genes! Meiosis 2 Sister chromatids separate into 4 different gametes, randomly. 23 duplicated Each gamete has a unique combination of genes! 23 unduplicated chromosomes in each gamete

Meiosis 1 & 2 - Females (Eggs) and Males (Sperm)

What creates genetic variability? Crossing over - switching of genes during meiosis 1 creates a unique combination of genes Independent Assortment - chromosomes separate into gametes randomly during meiosis 1 and meiosis 2 Random Fertilization - random sperm and egg combine to make a unique gamete