Looking at the pictures, identify the celebrity’s parent.

How about siblings?

Let’s think… What kinds of things did you look at to help you figure it out?

Let’s think some more… Why do these celebrities look the way they do? Why do YOU look the way you do?

It’s because you inherit traits from your mother and father. Traits – specific characteristic that varies from one individual to another (height, eye color, hair color, etc.)

Some Vocabulary Heredity – the passing on of characteristics from parents to offspring. Genetics – the study of heredity

Meiosis Review We know from meiosis, each human body cell contains 46 chromosomes and each human sex cell contains 23 chromosomes. During fertilization, a sperm carrying 23 chromosomes combines with an egg carrying 23 chromosomes

Each one of the 23 chromosomes from the father is going to find its matching chromosome from the mother. Homologous Chromosomes – pairs of chromosomes that are the same size and carry the same genetic information

The fertilized egg now has 23 pairs of chromosomes Half of the chromosomes came from the father while the other half came from the mother Each of these chromosomes is made of segments of DNA called genes that codes for a specific trait (we already know this!)

What are alleles? Allele – different versions of a gene for the same trait Some alleles can prevent other alleles from showing their traits. These are called dominant alleles. If the dominant allele is present, it will be expressed. The alleles that do not always show their traits are called recessive alleles. If both recessive alleles are present, it will be expressed

Genotype vs. Phenotype Genotype – the combination of alleles that make a person’s actual genetic make-up Example: Bb Phenotype – form of the trait that is observed Example: Brown eyes

Homozygous vs. Heterozygous Homozygous – When a person carries two of the same alleles for a trait B = Brown b = Blue Which is homozygous? BB Bb bb

Homozygous vs. Heterozygous Heterozygous – When a person carries one dominant and one recessive allele for a trait B = Brown b = Blue Which is heterozygous? BB Bb bb

Punnett Squares Punnett Square – a chart that shows all of the possible combinations of alleles that can result from a genetic cross.

Probability – a number that describes how likely it is that an event will occur BB – 25% Bb – 50% Bb – 25%

Let’s Try! In red-throated sapsuckers a red throat is dominant. A white throat is recessive. Write the genotype for: A homozygous dominant sapsucker A heterozygous sapsucker Draw a Punnett square showing their offspring Write the phenotypes and genotypes of the offspring What percentage of the offspring will have red throats? White throats?

Gregor Mendel Father of genetics Experimented with peas Used statistics to analyze and solve problems

Mendel’s Studies Why did Mendel study pea plants?

So... Why pea plants? Easy to identify traits Example: Tall or short, green or yellow seeds Short time between generations Produced a lot of offspring Easy to care for and control breeding

What traits did Mendel study Position of the flowers Height of plant Inflated or wrinkled seed pods Green or yellow seed pods Smooth or wrinkled seeds Seed color Flower color

Mendel was curious… If you cross pure bred tall plants (a tall plant with a tall plant), they produce tall offspring tall x tall = tall Same for pure bred short plants short x short = short But what about tall x short?

2nd cross (take the tall offspring from above) 1st cross tall x short = tall 2nd cross (take the tall offspring from above) tall x tall = short and tall plants Why?

Lets look at the parent plants They were purebred Always produce offspring that are the same as they are Homozygous – alleles are the same TT tt So we had a purebred (homozygous) tall (TT) cross with a purebred (homozygous) short (tt)

What about their offspring? TT x tt = Tall plants But what’s their genotype? Let’s do a Punnett square to find out!

Principle of Independent Assortment Genes for different traits (seed color vs. seed shape) separate independently during meiosis. A seed that is green and round does not always produce offspring that are green and round. Yellow and Round Green and Wrinkled

Dihybrid Cross R = Round Y = Yellow r = Wrinkled y = Green What would be the genotype for a round, yellow pea? What would be the genotype for a wrinkled, green pea?

Dihybrid Cross How can we set up a cross for a round, yellow pea (RRYY) and a wrinkled, green pea (rryy)? We can do a Punnett Square but it’s a little more complicated…

RRYY = Round, Yellow What are the possible gametes for this organism? If it was just a round pea (RR), what would the possible gametes be? R and R If it was just a yellow pea (YY), what would the possible gametes be? Y and Y

An organism with the genotype RRYY could form multiple gametes.

Dihybrid Cross RRYY RY, RY, RY, RY rryy ry, ry, ry, ry

Incomplete Dominance Incomplete dominance – when one allele is not completely dominant over another Blends the two phenotypes Red (RR) crossed with White (WW) = Pink

Codominance Codominance – both alleles contribute to the phenotype Red (RR) crossed with Blue (BB) NOT Purple! Red and Blue

Polygenic Traits Polygenic Traits – traits that are controlled by more than one gene

Sex-linked - genes that are found on the sex chromosomes (X and Y) - p Males – XY Because males only have one X chromosome, all x-linked alleles are expressed (even if they’re recessive) Females – XX Because females have two X chromosomes, they need both recessive alleles in order for that gene to be expressed

Sex-linked Traits Colorblindness Genotypes XrY – Male has it = it is expressed XRXR – Female does not have it XrXR – Female is a carrier, but it is not expressed XrXr – Female is a carrier, and it is expressed

Sex-linked Traits A male with colorblindess (XCY) and his wife, who does not have colorblindness and is not a carrier, have a daughter. What is the daughter’s genotype? Is she colorblind?

Sex-linked Traits The daughter grows up and meets a nice young man who is not color blind. They get married and decide to have children. Is there a possibility that they could have a colorblind child?

Multiple Alleles Multiple Alleles – many genes have more than just two alleles that are possible Blood type A - Dominant B - Dominant O - Recessive

Blood Typing A woman who is Type AB has a child with a man who is Type AB. What are the possible genotypes of the child? What are the possible phenotypes?

Blood Typing What is the chance that a Type O and Type AB couple could produce offspring with Type A?

Pedigree Pedigree – a diagram that follows the inheritance of a single gene through several generations of a family Square – Male Circle – Female Solid – Has phenotype Empty – Does not have phenotype Horizontal line – connects parents Vertical line - offspring

http://hess. wiki. cvsd. k12. pa http://hess.wiki.cvsd.k12.pa.us/file/view/Pedigree+practice+worksheet.pdf

Pedigree

The Royal Family…

Karyotyping

What do the chromosomes look like? Karyotype – a picture of all the chromosomes in a cell arranged in pairs

Karyotyping

Chromosomal Disorders Nondisjunction – when homologous chromosomes fail to separate in meiosis. If nondisjunction occurs, an abnormal number of chromosomes may end up in the gametes Down Syndrome – 3 copies of Chromosome 21

Trisomy 21 - Down’s Syndrome 1 per 1000 births Physical and intellectual disabilities

Turner Syndrome Caused by the absence of an X chromosome – nondisjunction in the father Short stature, swelling, broad chest, low hairline, low-set ears, webbed neck, non-working ovaries – amenorrhea and sterility

Trisomy 18 – Edward’s Syndrome 1 in 6000 – 80% female Majority die before birth Heart defects, kidney malfunctions, intestines protruding from outside body