heredity and genetics. heredity 1. is it possible for two parents with blue eyes to have a brown...

Heredity and GeneticsHeredity and Genetics

HeredityHeredity1. Is it possible for two parents with blue

eyes to have a brown eyed child? 2. Is it possible for two parents with

brown eyes to have a blue-eyed child?

Discuss this with your group. Come to a decision and be prepared to explain the reasoning behind your answers.

Warm-up Warm-up

What have we learned so far about each of the following:

DNAGenesChromosomes

ChromosomesChromosomes have genetic have genetic information and are passed to information and are passed to offspringoffspring

Dividing onion cells

chromosomes

ChromosomesChromosomes have genetic have genetic information and are passed to information and are passed to offspringoffspring

Human chromosomes stained with a special chemical and viewed under a high-powered microscope

What exactly are chromosomes?

How do chromosomes contain genetic information?

Chromosome structure- Chromosome structure- DNADNAChromosomes = long pieces of

DNA

Chromosome structure- Chromosome structure- genesgenes

Human chromosome # 7

Contains about 1,800 genes

Contains over 150 million nucleotides

Link to view genes and DNA sequence

• Parts of chromosomes are called genes• Genes help determine your characteristics

– what are some example characteristics?

Trait – a characteristic of an organism◦Example: flower color

Gene – part of a chromosome that helps determine a specific trait◦Example: flower color gene

Allele – a form of a gene ◦Example:

One allele is the “blue” form of the gene One allele is the “red” form of the gene

Chromosomes come in Chromosomes come in pairspairs

Cut out from picture and match each in pairs

How many chromosomes?How many chromosomes?Humans = 23 chromosome pairs, or 46 total. We think we have about 40,000 genes.

Pea flower = 7 chromosome pairs (14 total)

Fruit fly = 4 chromosome pairs (8 total) 13,601 genes identified so far!

Potato = 24 pairs (total 48)Horse = 32 pairs (total 64)

Chromosomes come in Chromosomes come in pairspairsYou get one copy of a chromosome

from one parent and one copy of a chromosome from the other parent.

This pair of chromosomes is called a “homologous pair” because they have the same genes on them -

Flower chromosome 3

(from computer simulation)From Dad

From Mom

flower color gene

Chromosomes come in Chromosomes come in pairspairs

IMPORTANT: homologous pairs have the same genes, but they are NOT IDENTICAL◦Alleles can be different

From Dad

From Mom

flower color gene

“Blue” alleleof flower colorgene

“Red” alleleof flower colorgene

The combination of alleles The combination of alleles determines the observed determines the observed characteristicscharacteristics

REDalleleChromosome

combination

Allelecombination

Observedcharacteristic

RED allele

REDallele

BLUE allele

BLUEallele

BLUE allele

red, red red, blue(or blue, red)

blue, blue

RED RED BLUE

Dominant and recessive Dominant and recessive allelesallelesOnly one red allele is needed for

the flower to look red.Scientists call this a DOMINANT

allele

Two blue alleles are needed for the flower to look blue.

Scientists call this a RECESSIVE allele

Symbols used for allelesSymbols used for allelesThe traditional symbols used for

alleles are big and small lettersThe letter chosen usually refers

to the dominant alleleExample: R = Red allele

r = Blue allele


REDalleleChromosome

combination

Allelecombination


RED allele

REDallele

BLUE allele

BLUEallele

BLUE allele

red, red red, blue(or blue, red)

blue, blue

RED RED BLUE


RChromosomecombination

Allelecombination


RR Rr rr

RED RED BLUE

R R r r r

Phenotype – the observed (or measurable) trait of an organism that relates to one gene

Genotype – the two alleles that an organism has for a trait

Example: Trait = “flower color”Phenotype = “RED” or “BLUE”Genotype = “RR” or “Rr”

or “rr”



Allelecombination


RR Rr rr

RED RED BLUE

R R r r r



GENOTYPE

PHENOTYPE

RR Rr rr

RED RED BLUE

R R r r r

Homozygous – the two alleles are the same

RR and rr are homozygous genotypes

Heterozygous – the two alleles are different

Rr is a heterozygous genotype

heredity and genetics. heredity 1. is it possible for two parents with blue eyes to have a brown...

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