Mental Warm-up reflection (Question of the Day) 1/27/2015

Sexual reproduction is when a new organism is made using genetic information from two parents. •Why do siblings (brothers and sisters)

not all look exactly like either each other or either of their parents?

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homework

Introduction to Genetics

• Chapter 11.4 in the text bookMeiosis—a special type of cell division that

produces gametes which have half of the DNA of the body (somatic cells).

Fertilization—combining one sperm and one egg to generate a zygote (1st cell of the embryo).

Mitosis—growth of the zygote by asexual cell division.

Assortment of chromosomes into offspring during meiosis determines the inheritance of traits by offspring of sexual organisms.

The karyotype below, made from a developing human embryo, shows that a child inherits 23 pairs of chromosomes: 1 each from mom & dad. Colors are due to DNA probes (tags) that match similar sequences of DNA.

http://learn.genetics.utah.edu/content/chromosomes/intro/

Each chromosome carries a particular set of genes, always in the same places. Your body (somatic) cells contain two copies of each chromosome, so two copies of each gene; this is called diploid.

What is the diploid (2n) number of chromosomes in humans?

46

How many pairs of homologous chromosomes do humans have?

23 pairs Telomeres of the longer q arms

Telomeres of the shorter p arms

Paired sister chromatids

centromere

http://learn.genetics.utah.edu/content/chromosomes/readchromosomes/

The chromosomes of a somatic cell diagrammed below are arranged in a karyotype, the 46 chromosomes have been arranged in homologous pairs.

The paired chromosomes (for example, pair #1 or pair #2) are homologous chromosomes; this means that they are long double helices of DNA that: 1)

are the same length; 2) contain the same genes in the same order; and 3) are connected at their centromeres at the same location

Chromosomes number 1 - 22 are called autosomal (somatic or body) chromosomes.

The 23rd pair of chromosomes determines the sex of the individual and are called sex chromosomesThe sex chromosomes of a female human are

XX.The sex chromosomes of a male human are XY.

• What is the sex of person A? male

• How do you know? Y Chromosome

• What is the sex of person B? female

• How do you know? X Only

• Are the X & Y chromosomes the same size and shape? NO—Y is smaller because it contains fewer

genesWhat is the diploid number of chromosomes of person A?

46What is the diploid number of chromosomes of person B?

46

Sexual reproduction is made possible by a process called meiosis that halves the number of chromosomes while generating special reproductive cells called gametes or sex cells. Male gametes are called sperm, while female gametes are called eggs or ova.

Gametes receive one member of each homologous pair from the parent’s somatic cells. This means that somatic cells are diploid (2n) since they have 2 pairs of homologous chromosomes, but gametes are haploid (1n) since they do NOT contain homologous pairs—just one of each!

http://learn.genetics.utah.edu/content/inheritance/intro/

X

XEgg 1n karyotype 1n=23

Sperm 1n karyotype 1n = 23

Somatic cell karyotype for a female (above), for a male (below) 2n=46

Meiosis is a type of cell division that results in your giving one of each chromosome to your child in a sex cell, sperm or egg.Having one copy of each chromosome is called haploid.

Law of random segregation (one parental homologous chromosome, but not both, is passed into each gamete;

it’s random whether the maternal or paternal

chromosome will be passed)

Law of independent assortment

(the combination of maternal & paternal

homologues passed to each gamete is unique)

3 sources of genetic variation in gametes for sexual reproduction

Learn.genetics.utah.eduTour of the basicsWhat is heredity?

formation of gametes with one or the other, but not both, homologues==random segregation

mixing up the set of your paternal & maternal chromosomes during meiosis 1 ==independent assortment

3rd source of variaton: formation of tetrads (both homologues on same

spindle, exchanging matching genes) during cross over

4th source of variation—mistakes in DNA copying (DNA replication)

called mutations

• 5th source—random use of gametes made• 6th source—different mate combinations

Asexual reproduction or growth/repair of organisms utilizes mitosis (think My—

two—sis)

1 cell divides into two genetically identical daughter cells

Mitosis generates two genetically identical cells because the 2 copies of each chromosome are separated into two new daughter cells. The original cell is called the mother

cell.

The only reason mitosis generates genetic differences is mistakes in copying DNA

• Mutations

• Mutations are sometimes bad, but sometimes they generate helpful or harmless differences alleles giving unique traits.

Stages of mitosis from mother cells to genetically identical to 2 daughter cells.

http://highered.mcgraw-hill.com/sites/0073031216/student_view0/exercise13/mitosis_movie.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html

For sexual reproduction specialized cells called gametes (male sperm, female eggs) are required

These cells must have only 1 copy of each chromosome, not 2

Meiotic (meiosis, think my-o-sex) cell division generates 4 gametes with only 1 copy of each of the parent’s original pair of homologous chromosomes

How? Copy the DNA once, then divide twice.

Meiosis is a type of cell division that results in your giving one of each chromosome to your child in a sex cell, sperm or egg.Having one copy of each chromosome is called haploid.

Law of random segregation (one parental homologous chromosome, but not both, is passed into each gamete;

it’s random whether the maternal or paternal

chromosome will be passed)

Law of independent assortment

(the combination of maternal & paternal

homologues passed to each gamete is unique)

Meiosis (think My-O!-4-sex) Mitosis (think My-2-sis)Asexual reproduction most often used in unicellular organisms

Produces 2 somatic daughter cells

1 Diploid2 diploid cells

Copy DNA once, divide up copied DNA once

Genetically identical cells

No crossing-over

No random assortment

No random segregation

Occurs in all of the body except sex organs

For growth, repair, asexual reproduction

Sexual reproduction most often used in multicellular organisms

Produces 4 sex cells called gametes

1 Diploid4 haploid cells

Copy DNA once, divide up copied DNA twice

Genetically unique cells

USES crossing-over

USES random assortment

USES random segregation

Occurs only in sex organs

For making gametes only

Mitosis bothmeiosis

Mit-2-sis eukaryote cell division My-oh!-4-sexAsexual produces new cells sexualProduces 2 somatic cells replicate DNA once produces 4

gametes

1 Diploid2 diploid use a spindle 1 diploid4 haploid

1 round division2 rounds division

Genetically identical genetically unique

No crossing-overcrossing over

No random assortmentrandom assortment

No random segregationrandom segregation

In all of the body except sex organs in only sex organs

For growth, repair, asexual reproduction for sexual reproduction only

II. Pedigree NotesA “family tree” record that shows how a trait is inherited over several generations is called a pedigree.

Pedigrees are very helpful because they allow people to trace genetic disorders over several generations.

Symbols you will need to know:

1. A represents a Male and a represents a Female.

2. A shaded represents a Male with the trait

but a white represents a Male without trait.

3. A shaded represents a Female with the trait

but a white represents a Female without trait

4. Sometimes a square or a circle is partially shaded (half shaded), this means that the individual is heterozygous for a recessive allele. (They are known as “carriers” and their gentotype is Aa.)

5. A marriage is symbolized by a straight line.6. Offspring are symbolized by brackets underneath

the parents

I.

II.

III.

What do the Roman numerals symbolize? Generations

Do you remember? – is having hitchhiker’s thumb a dominant or a recessive trait

Final challenge:

Can you give the genotypes for each person in Mr. Heilemann’s family? Next to where you wrote each person’s name, give the genotypes (using N” and “n” – remember, each person has TWO alleles for this trait.