Introduction to Genetics Chapter 11

Look around the room… What color is your hair? Look at the chart and write down your hair color. Write down the colors of your classmates. Your parents? Your siblings? At home – look at the hair color of your biological parents. At home – look at the hair color of your biological siblings. Write them down.

Add up the numbers: Total class: # of top row: # of bottom row: Total parents: # of top row: # of bottom row: What do you notice about parents & children?

What do we see? Do we see the gene? We see brown pigment. Some forms of the gene cause more pigment to be made. Some forms of the gene cause less pigment to be made. Which is dominant? How can you tell? Darker hair is dominant to lighter hair because the enzyme makes more of the pigment.

Look at one family example: Squares are male Circle are female

Genetics study of heredity –Heredity: how traits are passed from parent to offspring –Traits: physical properties (color, height, texture, shape) These traits have different forms –Dark brown/medium brown/light brown, tall/ short, soft/hard –Different forms called Alleles

Gregor Mendel Scientist that performed experiments to find out how pea plants inherit traits in 1840’s

Mendel’s 1 st Principle Genes are chemical factors that control each trait of a living thing. –Inherited from parents –1 factor from mom & 1 factor from dad –Each factor you get is called an allele Allele = a discrete form of a gene Ex. Dark brown allele from mom & Light brown allele from dad

Example You have a gene for ear lobe shape Alleles are Free or Attached

Discussion What does meiosis have to do with the different traits siblings have?

Mendel’s 2 nd Principle When there are two or more forms (alleles) of the gene, some forms may be dominant & others may be recessive. Law of Dominance

Alleles Alleles have different strengths, or way to express themselves. –Dominant alleles are always expressed when present –Recessive alleles will only be expressed if no dominant allele is present

Trait Dominant Phenotype Recessive Phenotype color of irisnot blueblue widow's peakpeakno peak cheek dimplesdimplesnot dimples face frecklesfrecklesno freckles mid-digit hairhairno hair Hitchhiker's thumb straightcurved ear lobesfreeattached tongue rollingabilityno ability cleft chincleftno cleft Some common human traits

Mendel’s 3 rd Principle For organisms that reproduce sexually, adults have two copies of genes. These separate from each other in gametes. Law of Segregation

Example Remember making gametes? The 2 copies separate

Mendel’s Last Principle Genes for different traits can separate independently of each other during gamete formation. Theory of Independent Assortment ( like shuffling chromosomes into the eggs..just need one of each)

Example Remember making gametes? Genes for different traits

How do these principles help us? Make Predictions Parents alleles Offspring alleles We use Punnett Squares to do this!

How to make a Punnett Square… 1.Each side of the square represents the possible alleles parents could have in their gametes 2.We use shorthand to name traits 1 st letter of the dominant trait Dominant = CAPITAL Recessive = lowercase GG g G

How to make a Punnett Square cont… 3.We will also use some new vocab words to compare your alleles Homozygous = same letter (GG or gg) Heterozygous = different letters (Gg) Genotype = the letters (GG, gg or Gg) Phenotype = physical appearance (Green)

Not all 23 Chromosomes are homologous… You have two chromosomes that don’t match each other… Therefore, you don’t have a genotype like GG or gg or Gg…

Autosome vs. sex chromosome Autosome chromosome that is not involved in sex determination homologous Sex Chromosome determines the sex of the organism non-homologous p 341

Karyotypes – pictures of your chromosomes

Sex Determination The X-Y system XX = female XY = male The presence or absence of the Y chromosome determines the gender

Sex-Linked Inheritance

So sex-linked genes… Genes found on X or Y chromosome –We will study traits on the X Females – XX (works the same) –Write like exponent X G X g Males – only one X –There is no heterozygous (Gg) –Write like exponent X G y –No letter on the y p 350

Sex-linked genes (cont) X-linked recessive traits appear more often in males –Only need to inherit one allele instead of the usual two Example in humans – color blindness

The Punnett Square!! Female XX Male XY X XX XX X X X X Y Y Y

Hemophilia, a genetic blood disorder, is caused by a recessive sex-linked gene. A phenotypically normal couple had a son with hemophilia. –What is the probability that their next child, if a girl, would also have hemophilia?

Other Types of Inheritance

Principle of Dominance At the protein level –BB = both genes produce protein that creates black pigment –bb = both genes produce an inactive protein –Bb = B gene produces black pigment, enough to see black despite the inactive b allele

Incomplete Dominance Active (dominant) allele does not fully compensate for the inactive (recessive) allele Heterozygous results in an intermediate phenotype –NOT blending –the recessive phenotype can reappear in the next generation four o’clocks

RR = red Rr = pink rr = white 4 O’clocks

In 4 O’clocks, red is dominant over white flowers. Incomplete dominance results in a pink color flower. What would the phenotypic ratio be for a cross between a plant with red flowers and one with white flowers?

Codominance Both alleles fully expressed –Examples Calico cat –Fur is black, orange, and white Calico is a coat color found in cats, which is caused by a SEX-LINKED, CODOMINANT allele. B = black, R = orange, and BR = calico. The following genotypes are possible; Female cats can be black X B X B, orange X R X R, or calico X B X R Male cats can be black X B Y or orange X R Y Sickle cell disease (pg. 347) H A H S A=normal S=Sickle H means hemoglobin Cats have 19 pairs of chromosomes

Coat color in cattle is codominant. Red is dominant, white is recessive, and a roan cattle has red and white patches. What is the result of a cross between a red cow and a roan cow?

Polygenic Inheritance Trait is determined by multiple genes (not just one) Produces a wide range of variations in phenotypes –Height –foot size –Hair color –metabolism

Multiple Alleles One gene that has three or more alleles –Normally we have seen two – B & b Each allele produces a distinct phenotype –Now we will use a different letter for each allele or discrete form of the gene. Ex: Human Blood Groups – ABO system

Human Blood Groups Blood type is determined by 2 factors – ABO and Rh factor ABO system represents multiple alleles AND codominance –You can make an A, a B, or nothing which is O – that’s the multiple alleles part –A and B are codominant, so if you have one of each, you express both (O is recessive)

What are these A’s & B’s ? Antigens = molecules on Cells Can have A, B, AB or O blood type Blood type corresponds to your antigens

What are antigens? Blood cells produce molecules called antigens that sit on their surface. These antigens help the blood cells to defend themselves by acting as signals to the immune system. If you make antigen A, then your body sees only that as normal & will see anything else as an intruder If your body thinks it sees an intruder, it makes antibodies that will kill that antigen

Writing Blood Types  I A = A (A antigen)  I B = B (B antigen)  I A I B =AB ( both antigens)  i = O (no antigens) Separate gene This is simple dominant and recessive inheritance  ++ = Rh positive  +- = Rh positive  -- = Rh negative - you don’t make this antigen Part 1 – the letterPart 2 – the Rh factor

Blood Type Donor Blood Type PhenotypeGenotypeAntigensAntibodiesABABO Type AIAiIAi IAIAIAIA Type BIBIBIBIB IBiIBi Type ABIAIBIAIB Type Oii

Pedigree Analysis It “runs in the family” If you know whether a trait is dominant, recessive, etc… –You can determine how likely your offspring is to have that trait. This chart shows Major trends: –Dominant  seen in every generation –Recessive  “skips a generation”

Pedigree Symbols

Hemophilia

Common Human Genetic Disorders Dominant –Huntington Disease –Rh factor in blood –Achondroplasia Recessive –Cystic Fibrosis –Albinism Sex-Linked Recessive –Colorblindness –Hemophilia –Muscular Dystrophy Co-Dominant –Sickle Cell Anemia –A&B in blood groups Multiple Alleles –ABO blood groups Polygenic –Height –Weight –skin color