GB Unit 4

chromosomes

• large piece of DNA w/ genes on it

genes

• piece of info. that encodes for a trait

• more than one chromosome in them

chromatin

• all chromosomes congregated in the nucleus, consisting of DNA and proteins

• protein embedded on DNA —> can coil DNA into thicker bundle that’s shorter in length

mitosis

• Asexual

• division of material in nucleus

• M phase

• one 2n cell divides into 2 2n cells

• form of cellular reproduction for growth and repair

Cytokinesis

• cell physically divides into 2

Meiosis

• sexual

• 2n cells produce 1n cells

• used to reduce the chromosome number during the development of sperm and egg

• must keep 46 chromosomes

Zygote

• fertilized egg

• has copies of mom (1 copy/ 1n) + dad (1 copy/ 1n) chromosomes —> 2n

• 23 chromosomes + 23 chromosomes

- ½ genetic info…keep gen to gen consistent + mix up gene pool

sister chromatids

• direct, identical copies of a particular chromosome

• start with 1 chromatid

• DNA replication happens

• now we have 2 chromatids/ singular duplicated chromosome/ sister chromatids

• mitosis happens and the sister chromatids are pulled apart at the centromere

• now we have daughter chromosomes that are genetically identical

centromere

• chromosomal region where chromosomes of a particular type join for cell division

homologous chromosomes

• chromosomes of the same type of chromosome, but from a different parent

• NOT IDENTICAL

• ex: eye color chromosome are slightly different between mom and dad

steps of mitosis

• premitotic

• prophase

• metaphase

• anaphase

• telophase/cytokinesis

Interphase

• G1, S, G2

• eukaryotic cell duplicates the contents of the cytoplasm

• DNA replicates in the nucleus

Prophase

• chromosomes condensing (winding up → fatter, coiled)

• 2 sister chromatids held together at centromere

• outside the nucleus, the spindle starts to assemble between centrosomes

• spindle fibers from each pole attach to the chromosome at protein complexes on each side of the chromosome chromosome moves toward one pole, then toward the other

metaphase

• spindle fibers connect to centromeres

• all 46 sister chromatids line up in middle of cell

anaphase

• sister chromatids separate and become daughter chromosomes

• the spindle fibers disassemble and each pole gets a set of daughter chromosomes

  

telophase

• spindles disappear and new nuclear envelopes form around daughter chromosomes

• division of cytoplasm begins

what is the main difference between meiosis I and meiosis II

• I: separating homologous chromosomes

• II: separating sister chromatids

Meiosis I: Prophase I

Tetrads form, and crossing-over occurs as chromosomes condense; the nuclear envelope fragments

Meiosis I: Metaphase I

• Tetrads align at the spindle equator. Either homologue can face either pole

Meiosis I: Anaphase I

• Homologues separate, and dyads move to poles

Meiosis I: Telophase I

• Daughter nuclei are haploid, having received one duplicated chromosome from each homologous pair

Meiosis II: Prophase II

• Chromosomes condense, and the nuclear envelope fragments.

Meiosis II: Metaphase II

• The dyads align at the spindle equator.

  

Meiosis II: Anaphase II

• Sister chromatids separate, becoming daughter chromosomes that move to the poles.

  

Meiosis II: Telophase II

• Four haploid daughter cells are genetically different from each other and from the parent cell

How many divisions in mitosis v. meiosis

• 1 v 2

How many daughters per cells cycle in mitosis v. meiosis

• 2 v 4

where does mitosis and meiosis occur in?

• somatic

• germline

Nondisjunction

(Chromatids/Chromosomes fail to separate) - generally lethal

Trisomy

• three copies of a chromosome

Monosomy

• single copy of a chromosome

how can there be changes in chromosome number in Meiosis I and II

• both members of a pair go into the same daughter cell

• sister chromatids fail to separate

Modes of inheritance

• patterns in which single-gene traits and disorders occur in families

Cystic fibrosis

• autosomal recessive (need cc to have)

• Affects both sexes and can skip generations through carriers

1. Respiratory tract wants to stay liquid…lungs pump salt into mucus → osmosis —> water goes into mucus

2. CF —> missing gene for protein from both parents —> can’t make protein…mucus dries out easily

what do genes encode for?

• proteins

Independent assortment

• Ex: what purple and white do independent of short and tall

• Ex: having a boy as a first child doesn’t impact the chances of the next child being a boy

Mendel’s First “Law”

• Segregation

• hybrids hide one expression of a trait

• reappears when hybrids are self-crossed

• each element was packaged in a separate gamete

Principle of segregation

• Mendel’s idea that each element (gene) separates in the gametes. This reflects the actions of chromosomes and the genes they carry during meiosis

Product Rule

Ex:

1. probability of having a girl = ½

2. probability of having another girl = ½

3. probabilty of having 2 girls = ½ x ½ = ¼

Homozygous

• carry same alleles TT or tt

Heterozygous

• carry different alleles Tt

Genotype

• Organism’s alleles

Phenotype

Outward expression of an allele combination

Wild Type

• Most common phenotype (Recessive or dominant)

Mutant phenotype

• Variant of a gene’s expression that arises when the gene
  undergoes mutation

Autosome

• genes are here

• non sex chromosome

• chromosomes 1-22

sex chromosome

• gene here

• X and Y

For Autosomal Dominant and Recessive inheritance what is the difference between the frequency that males and females are affected?

• they’re both affected with equal frequency

How does Autosomal Dominant inheritance move through generations?

• successive generations until no one inherits the mutation

Does someone with Autosomal dominant inheritance have an affected parent?

• YES unless they have a new mutation

How does Autosomal recessive inheritance move through generations?

• can skip generations

Does someone with Autosomal recessive inheritance have an affected parent?

• they have parents who are affected or who are carriers

Achondroplastic dwarfism

• caused by a gain-of-function mutation in a gene (FGFR3) that normally inhibits growth of the long bones of arms and legs

• Autosomal Dominant

• BUT if you’re AA, the skeletal defect is so severe that it wouldn’t survive embryonic development

• So…

• Aa x Aa

1. AA

2. Aa

3. Aa

4. aa

—> AA never born

probability of not having dwarfism goes from 2/3 to 1/3

do most traits follow Mendel’s patterns? why?

• no

• polygenic: MANY genes that contribute to a trait

• environment plays a role as well