Sexual Reproduction

Let’s Review!

Mitosis is:

When a cell makes a copy of itself for:growthrepairreplacement

In mitosis:

Mother cell with a full set Of chromosomes (diploid number; a.k.a. 2n)

Two daughter cells With a full set of Chromosomes(diploid number; a.k.a 2n)

The Phases of Mitosis

Prophase Metaphase Anaphase Telophase Cytokinesis(you should ALL know these by heart by now!)

Mitosis

Only body cells reproduce by mitosis (and some organisms too but we will talk about that later)

Chromosomes Homologous

chromosomes: the chromosomes that make a pair They have the same

length and same centromere position, and control the same inherited trait

Gametes

Sex cells that have half the # of chromosomes Ensures that an organism has the same

number of chromosomes from generation to generation

In humans, each gamete has 23 chromosomes n = number of chromosomes in a

gamete

Gametes Haploid: n Diploid: 2n (female n + male n)

When 2 human gametes combine through fertilization, 23 homologous chromosomes are formed

Meaning…Mom has 23 chromosomes

Dad has 23 chromosomes

You have 46 chromosomes

Meiosis

Process that creates gametes Cell division that REDUCES the

number of chromosomes Occurs in reproductive structures Mitosis maintains chromosome # Meiosis reduces it by half by splitting

homologous chromosomes 2n n

Meiosis I and II

Interphase

Replication of DNA Protein synthesis

Meiosis I

Prophase I: Crossing over:

chromosome segments are exchanged between homologous chromosomes

Centrioles move to opposite poles

Spindle fibers form and bind to sister chromatids at the centromere

Meiosis I Metaphase I: Homologous

chromosomes line up at center of cell Anaphase I: Homologous chromosomes

separate and pulled to opposite ends of cell, chromosome # is reduced from 2n to n

Telophase I: Chromosomes reach poles Each pole contains only one chromosome of

the original homologous chromosomes

Meiosis II

Prophase II: chromosomes condense Metaphase II: HAPLOID number of

chromosomes line up at the equator Anaphase II: sister chromatids are

pulled apart Telophase II: chromosomes reach

poles and nuclear membranes and nuclei form

Meiosis II

The chromosomes DO NOT replicate between I and II

End result is 4 haploid cells, each with n number of chromosomes

http://www.pbs.org/wgbh/nova/miracle/divide.html

Sexual vs. Asexual Reproduction Asexual

The organism inherits all of its chromosomes from one parent

Individual is genetically identical to its parent

Mendelian Genetics

Genetics

Genetics: the study of heredity

Heredity: the passing of traits from parent to offspring (INHERITANCE)

Father of Genetics

Gregor Mendel Austrian Monk who

experimented with garden peas in 1866

Noticed certain traits seemed to be passed from one generation to another

Mendel Mendel worked with peas Peas self-fertilize Noticed some varieties

always made green seeds, and some always made yellow seeds

Mendel cross-pollinated the peas by hand

Peas

Parent Generation (P): 1st line of crosses

First Generation(F1): offspring of the parent generation

F2 Generation: second cross, using the F1 offspring

He concluded…

There must be TWO forms of a gene controlled by different factors

ALLELES: alternative form of a single gene

For example, the gene height Tall or short

Alleles

Dominant: represented by a capital letter (T = tall This is the trait that is seen

Recessive: represented by a lowercase letter (t = short) This trait is not seen, it is masked by the

dominant allele ~ it’s there, just hidden!

Dominance

If the dominant allele is present, it will show up

There must be 2 recessive alleles (one from each parent) in order to show up

Alleles Since alleles are inherited from each

parent, they can be the same or different Homozygous: individual inherits 2 of the

same allele TT – homozygous dominant tt – homozygous recessive

Heterozygous: individual inherits 2 different alleles, one dominant and one recessive Tt

Since the dominant allele is present, it will show

So…

If presence of dimples is a recessive trait, and no dimples is dominant, what alleles would you see for – An individual with dimples An individual without dimples

Genotype & Phenotype

Genotype: organism’s allele pairs Heterozygous,

homozygous dominant, or homozygous recessive

Phenotype: observable appearance of genes

Putting it all Together…

ALLELE ALLELE

GENOTYPE (HETEROZYGOUS)

Tt = TallPHENOTYPE

Law of Segregation

Two alleles for a trait separate during meiosis Each gamete will have a different allele

They will be reunited during fertilization

Punnett Square

Used to predict the possible offspring between two known genotypes

Monohybrid: crossing one trait at a time

Punnett SquareP

aren

t 1- P

ure

Sho

rtParent 2 – Pure Tall

F1 Generation

Tongue Rolling

Dominant Trait ~ T 2 parents are heterozygous (Tt) for

the trait What possible phenotypes will their

children have?Tt

tT

TtTT tt

TtTongue

rollerTongue roller

Tongue roller

Non-tongue roller

Law of Independent Assortment

When your body makes gametes (during meiosis), your gametes only get one copy of each gene

Whatever copy goes into the gamete is random; the inheritance of one gene does not influence the inheritance of another gene; they are independent Every person with brown hair doesn’t have brown eyes

Some genes are inherited together (LINKED) because the genes are very close to each other on the chromosome. people with red hair are also fair-skinned.