Presentation is loading. Please wait.

Presentation is loading. Please wait.

Unit 3 Genetics.

Similar presentations


Presentation on theme: "Unit 3 Genetics."— Presentation transcript:

1 Unit 3 Genetics

2 What is Genetics? Genetics is the study of heredity.
Heredity is how traits are passed down from generation to generation. Gregor Mendel “Father of Genetics”. He studied the way characteristics are passed on in pea plants in the 1800’s.

3 Mendel’s Discovery Mendel discovered that a pea plant’s characteristics such as height, seed color and pod color are determined by an inheritance factor. He observed 14 different characteristics These inheritance factors where later called genes. Genes are a unit of heredity. They contain the instructions for a trait. A trait is a characteristic (color, height) coded for by two or more genes.

4 Fourteen Traits of Pea Plants:
Flower Color Pink Flower White Flower Seed Color Yellow Seed Green Seed Seed Shape Round Seed Wrinkled Seed Pod Color Green Pod Yellow Pod Pod Shape Smooth Pod Wrinkled Pod Flower Position Along Stem At the Tip Plant Size Tall Plant Short Plant

5 Types of Genes Allele: 2 forms of a gene Dominant:
The gene that covers up the effect of the other one. Use a capital letter. Example “T” or “G” Recessive: The effect of the gene is hidden (unless two are present). Use a lower case letter. Example “t” or “g”

6 Mendel developed true breeding plants for each trait because true bred plants always gave the same results every time. PURE PURE PURE He found when breeding different pure forms of the same trait that one trait would always show up while the other one did not. It was for this reason that he labeled the trait that always showed up in these crosses DOMINANT and the trait that did not show up RECESSIVE RECESSIVE PURE DOMINANT PURE All Dominant But NOT PURE

7 He tested many characteristics and found that this was true for all of the traits. They had a dominant trait and a recessive trait. He did his experiment again using the offspring from the first cross. His results were very strange. From two parents showing the dominant trait, he got offspring that showed the recessive trait. WEIRD Not Pure Not Pure ???? Offspring from the Pink and White Cross This proved that the parents and offspring have 2 genes for each trait. How else could the parents have offspring that showed different traits than the parents.

8 Females are listed by XX.
DNA makes up genes. Genes make up chromosomes. DNA GENES Chromosomes There are 23 pairs (46 total) chromosomes in each non-sex cell for humans. 23 chromosomes in sex cells. Females are listed by XX. Males are listed by XY. Genetic disorders: Tay-Sachs: Caused by a gene mutation on chromosome 15 Down Syndrome: An extra copy of chromosome 21 is present. Look up other genetic disorders.

9 Describing Traits Traits are ways to describe living things. We are going to focus on human traits during genetics. Traits that we may discuss include: hair color, eye color, blood type. Phenotype: What the organism looks like. Its Physical makeup. Examples : Tall, Short, round or wrinkled Genotype: The genetic make-up of a trait. What 2-letter gene combination it is made from. Examples TT, Tt, tt

10 Cross Pure Tall with Pure Short
Punnett Square: Determine the probability that offspring will or will not have a given trait. Pure Tall plant ( T T ) crossed with a Pure Short Plant ( t t ) Each parent can give one trait gene to the offspring so each offspring will get half their trait genes from each parents. The chances of any parent giving a particular trait gene are random. We always start off with what we know in a KEY: Then we show the cross: Key: T- Tall Plant t – Short Plant Cross Pure Tall with Pure Short T T X t t The Pure Short parent can give a t or a t The Pure Tall parent can give a T or a T. We put these on a grid and see what possible outcomes we can get…

11 T T X t t t t t t t t T T T T T T T The Phenotype of the offspring is:
One parent goes on the top of the box and the other goes on the side T T T T X t t t T t T t You fill in the squares with the appropriate letter The possible offspring will appear in the boxes By looking at these results, you can see that the offspring will all be Tall but not Pure Tall. They are all mixed. This is called Hybrid. T t T t The Phenotype of the offspring is: 100 % TALL The Genotype of the offspring is: 100% mixed… We call this Hybrid T t

12 Describing Genes When we write genes we use one letter (G or g, T or t, etc.) Traits or characteristics are determined by one or more pair of genes. Half of your genes come from your mother and half of your genes come from your father. Purebred or Homozygous : Both genes are the same. Example: TT or tt are BOTH Homozygous. It doesn’t matter if they are dominant or recessive…just that they are the same. Hybrid or Heterozygous : Both genes are different. Example Tt is Heterozygous. Heterozygous offspring always show the dominant trait.

13 Punnett Squares practice
We looked at green seeds and yellow seeds. If both plants are homozygous, what are their genotypes? Key: G – Green seeds g – Yellow seed Plant 1 (green) = GG Plant 2 (yellow) = gg Identify the genes that are present in each plants’ sex cells. GG gg G G g g

14 We are now going to determine the possible genotypes and
We are now going to determine the possible genotypes and phenotypes of the offspring using a Punnett Square. GG x gg Genotype g g gg = 0/4 = 0% Gg = 4/4 = 100% Gg Gg G GG = 0/4 = 0% Phenotype Gg Gg G Green = 4/4 = 100% Yellow = 0/4 = 0%

15 GG Gg Gg gg G g G g Parents = Gg X Gg
Determine the genotype and phenotype probabilities for a cross between two heterozygous plants from the previous problem. Parents = Gg X Gg Genotype G g gg = 1/4 = 25% Gg = 2/4 = 50% GG Gg G GG = 1/4 = 25% Phenotype Green = 3/4 = 75% Gg gg Yellow = 1/4 = 25% g

16 When you look closely at it, there are only six crosses that deal with two alleles. They are: (using G and g as example traits) GG x GG Pure Dominant x Pure Dominant GG x Gg Pure Dominant x Hybrid GG x gg Pure Dominant x Pure Recessive Gg x Gg Hybrid x Hybrid Gg x gg Hybrid x Pure Recessive gg x gg Pure Recessive x Pure Recessive If you can memorize these six crosses and their phenotype and genotype ratios, you will never see a genetics problem you can’t solve. Also remember that anything crossed with a Pure Recessive is a Test Cross. It is a control to show what recessive traits you may have.

17 Practice Problem Mendel also studied the heights of pea plants during his experiments. He determined that tall pea plants were dominant over short pea plants. Step 1: Create a key. Pick a letter to represent genes. Dominant = Tall (T) Recessive = short (t) Use the key to help you answer the following questions: 1. Determine the phenotype of a plant that is Tt. 2. Determine the genotype of a homozygous small plant. 3. Would a heterozygous plant show the dominant or recessive trait?

18 Dominant = Tall (T) Recessive = short (t)
Determine the phenotype of a plant that is Tt. Phenotype means what it looks like. It will be tall because it has one dominant gene (T). 2. Determine the genotype of a homozygous small plant. Genotype means genetic make-up. Homozygous means the same and small is recessive (small letter).The answer is tt. 3. Would a heterozygous plant show the dominant or recessive trait? Heterozygous means different. (Tt) The answer is dominant because there is at least one big T. To show recessive you have to have two small t’s.

19 Vocabulary Practice Problems
1. Brown hair is dominant over blonde. A. Create a key for the traits. B. What would the genotype for a blonde be? C. What would the phenotype be for a person that is heterozygous? 2. Freckles is dominant over non-freckles. Mom is purebred for freckles. Dad is heterozygous for freckles. B. Determine the genotypes for Mom and Dad. C. Could any of their children NOT have freckles? Explain your answer.

20 Maybe Baby Directions 1. Determine baby’s gender:
Female: XX Male: XY Dad determines gender by flipping a coin: Heads: X Tails: Y 2. Name the child. (Use father’s last name) 3. Determine genes for the child Each partner flips a coin. Heads: 1st allele (A or L1) Tails: 2nd allele (a or L2) Circle all your results on data sheet You must flip the coin multiple times when there is more than one letter for a trait!!! Ex. Eye and hair color Three different letters means you flip three times!!!!!

21 Maybe Baby Directions 4. You now have to record the genotypes and phenotypes for the alleles you determined yesterday. Make sure you read carefully. Not all traits are going to be seen. Put NA in the genotype and phenotype box if that trait is not visible for your child. 5. Get your data sheet signed by the teacher after you sketch the characteristics. 6. Begin drawing your child as a teenager. USE PENCIL!!!! You need to draw front view and side view of your child. Your drawing must include: Your child’s name on the front. All 30 characteristics between the two drawings. Your name and your partner’s name on the back. Star your name on the back!!!!

22 1A. Key: B = brown = dominant
b = blonde = recessive 1B. Blonde is recessive. “bb” 1C. Heterozygous means different. Phenotype means what it looks like. “Brown hair” 2A. Key: F = freckles = dominant f = non-freckles = recessive 2B. Mom = FF Dad = Ff 2C. There is no possibility that any of their children could not have freckles. Mom has two big F genes, which means she will always give her children a F. Therefore all of the children will have freckles. You need two little f’s for non-freckles.

23 Pedigree Chart Follows the passing of a trait from generation to generation. Looks like a family tree. = male = female Shaded shape means that the recessive trait is expressed. Half shaded shape means that they are a carrier of the trait. Carriers have one gene but do not express or show the trait.

24 marriage Generation 1 parents Generation 2 children
Oldest child to the left Youngest child to the right Number of rows = number of generations Count from the top to the bottom

25 Normal skin is dominant over albino skin.
How many males? How many females? How many generations? How many marriages? 5 1 2 6 3 4 5 8 10 9 7 11 6 Nn 4 Nn 3 Nn N_ Nn nn Normal skin is dominant over albino skin. Key: Normal = N = dominant Albino = n = recessive Recessive trait is colored in! Nn nn nn N_ nn

26 Page 6 in Packet N = normal vision = dominant
n = nearsighted = recessive Shaded = recessive trait 1 2 nn N _ 4 3 N n nn 9 8 6 7 5 nn nn N n nn N n 11 12 10 Page 6 in Packet nn N n N n

27 Green seeds are dominant over yellow seeds
Green seeds are dominant over yellow seeds. A homozygous recessive plant (1) is mated with a homozygous dominant plant (2). Make a key. Determine the genotypes of the two plants. Determine the phenotype of the two plants. Could their offspring have yellow seeds? Explain. What is a trait? How many chromosomes do human sex cells have?

28 More Pedigree Practice
Dimples are dominant over non-dimples Shaded areas represent the recessive trait. Make a key! How many males? How many females? How many generations? How many marriages? How many children did the parents in the first generation have? How many males have dimples? How many females do not have dimples?

29 2 1 15 14 13 9 7 5 3 4 6 8 10 11 12

30 2 1 15 14 13 9 7 5 3 4 6 8 10 11 12 Dd dd Dd dd Dd dd Dd Dd dd dd dd
D = dimples = dominant d = non-dimples = recessive 8 males 7 females 3 generations 2 1 15 14 13 9 7 5 3 4 6 8 10 11 12 3 marriages 3 children 5 males have dimples 4 females don’t have dimples. Dd dd Dd dd Dd dd Dd Dd dd dd dd dd Dd Dd Dd

31 Pedigree Chart Practice
Widow’s peak is dominant over non-widow’s peak Make a key What is the dominant trait? Determine genotypes for all. 5. How many males have a widow’s peak? How many generations are there? 6. How many marriages are shown?

32 I II III IV Key: W= widow’s peak = dominant w = non- peak = recessive
c) 4 generations d) Having the widow’s peak is dominant. e) 5 males have a widow’s peak. f) 4 marriages Ww

33 Vocabulary Quiz Free (unattached) earlobes are dominant over attached earlobes. Mom is heterozygous and Dad is homozygous recessive. Use this information to answer the questions below. Make a key. Determine the genotypes: Mom = Dad = Determine the phenotypes: Is it possible for their children to have attached earlobes? Why or why not? What is the difference between a gene and a trait?

34 Make a key. How many marriages are present? How many generations are shown? How many males are albino? How many females are normal? How many children did 3 and 4 have in the first generation?

35 Genetics Vocabulary Problem
Red flowers are dominant over white flowers. A heterozygous plant (1) is crossed with a homozygous dominant plant (2). Make a key. What are the phenotypes of both plants? What are the genotypes of both plants? Is it possible for the new plants to have white flowers? Explain. What is the trait being studied? Who is Gregor Mendel? Why is he important?

36 Cell Division Mitosis: Occurs in body cells.
One cell divides into two. Both cells have the same genetic material as the parent cell. Four chromosomes Four chromosomes copied Four chromosomes go into each cell during division Four chromosomes in each identical cell

37 Cell Division Meiosis: Occurs in sex cells (egg and sperm).
One cell divides into four. The four daughter cells have ½ the genetic material as the parent cell. Stage 1: Stage 2:

38 Pedigree Chart Quiz Questions
Make a key. Determine the genotypes for each person using your key. How many males are there? How many females are there? How many marriages are present? How many generations are shown? How many males are PTC non-tasters? How many females are PTC tasters? How many children did 1 and 2 from the first generation have?

39 Tt tt tt Tt T t t t Parents = Tt X tt
Determine the genotype and phenotype probabilities for a cross between a heterozygous plant and a short plant. The trait we are studying is plant height. Tall is dominant over short. Parents = Tt X tt T = tall = dominant t = short = recessive Genotype T t TT = 0/4 = 0% Tt = 2/4 = 50% t Tt tt tt = 2/4 = 50% Phenotype Tall = 2/4 = 50% t tt Tt Short = 2/4 = 50%

40 Punnett Square Practice Problems
Normal skin pigment is dominant over albino. Show a cross of an albino man with a heterozygous normal woman. Brown eyes are dominant over blue eyes. Using a Punnett Square, determine the probability that the offspring will be homozygous recessive if both parents are heterozygous dominant. Determine the genotypes for the individuals in the pedigree chart below. Widow’s peak is dominant over non-peak. Make a key Determine genotypes Determine number of generations What is the dominant trait? How many males have peak? How many marriages?

41 n n Nn N Nn n nn nn 1. Key: N = normal = dominant
n = albino = recessive Parents: Male = nn Female = Nn n n Genotype NN= 0/4 = 0% Nn Nn = 2/4 = 50% N Nn nn = 2/4 = 50% Phenotype normal = 2/4 = 50% n nn nn albino = 2/4 = 50%

42 B b Bb B BB b Bb bb 2. Key: B = brown = dominant b = blue = recessive
Parents: Male = Bb Female = Bb B b Genotype BB= 1/4 = 25% Bb Bb = 2/4 = 50% B BB bb = 1/4 = 25% Phenotype brown = 3/4 = 75% b Bb bb blue = 1/4 = 25%

43 Parent cross = ________ x ________ Genotype
_____ = _______ = _____ % ______ ______ Phenotype _______ = _______ = _____ % ______

44 Red flowers is dominant over white flowers.
A plant (1) is homozygous dominant is crossed with a heterozygous plant (2). Use a Punnett Square to determine the probability that the offspring will be white. Use a Punnett Square to determine the probability the offspring will be white if two heterozygous plants were crossed. A homozygous dominant plant (3) is crossed with a homozygous recessive plant (4). Determine the probability the offspring will be red using a Punnett Square.

45 Tall is dominant over short. Recessive trait is shaded. 1
9 13 14 15 16 2 4 3 5 6 7 8 10 11 12 Make a key How many males are tall? Determine the genotypes. 5. How many females are short? How many marriages. 6. How many generations?

46 Vocabulary Quiz Free earlobes are dominant over attached earlobes. Mom is heterozygous and Dad is homozygous recessive. Use this information to answer the questions below. Make a key. Determine the genotypes: Mom = Dad = Determine the phenotypes: Is it possible for their children to have attached earlobes? Why or why not? What is the difference between a gene and a trait?

47 Sex-linked traits Sex-linked traits are caused by genes found on the X chromosome. Sex-linked traits are recessive. Fewer females are afflicted with these traits because they have two X chromosomes and the other is usually normal. Males only have one X chromosome, so when they inherit the sex-linked gene, they display the trait. Examples: color-blindness, hemophilia XX XX- X-X- XY X-Y Normal female Carrier female Afflicted female Normal male Afflicted male

48 Sex-linked traits practice problems
A man normal for blood clotting marries a woman who is a carrier for hemophilia. What are the chances they will have a child with hemophilia? Use a Punnett Square to prove your answer. What is the probability that a woman with normal vision who marries a color-blind man will have a color-blind child? A man with normal vision and a woman with normal vision have three sons. Two of the sons have normal vision and one of them is color-blind. What are the probable genotypes of the parents?

49 Intermediate Inheritance
Not all traits are either dominant or recessive. For some traits, heterozygous individuals are different than both homozygous parents. Codominance Incomplete Dominance Both alleles are blended in heterozygous offspring Both are different capital letters Both alleles are expressed in heterozygous offspring Both alleles are dominant Both are different capital letters Red flowers = RR White flowers = WW Pink flowers = RW Red coat = CR CR White coat = CW CW Roan coat = CR CW (both red and white are seen)

50 Multiple Alleles: Phenotype Genotype(s) A IA IA , IA i B IB IB, IB i
When there are more than 2 (multiple) alleles for a trait. Examples: Human blood groups have 3 alleles. (A, B, O) A and B are both dominant, O is recessive The possible combinations of these blood alleles are: Phenotype Genotype(s) A IA IA , IA i B IB IB, IB i AB IA IB O ii

51 Dihybrid Crosses Study two traits at the same time.
Determine the outcome for both traits together. A pure tall plant with blue flowers is mated with a short plant with white flowers. Determine the genotypes and phenotypes of the offspring. Tall and blue flowers are both dominant traits. TTBB X ttbb Parents: T = tall ttbb TTBB t = short tb tb TB TB B = blue b = white

52 Genotype Phenotype Tall and blue = 100% TtBb = 100% TtBb TtBb TtBb

53 Now mate two of the offspring to determine the possible genotypes and phenotypes.
EXTRA CREDIT!!! You must show ALL possible genotypes and phenotypes! Genotype TtBb X TtBb ttbb = 1/16 = 6.25% ttBb = 2/16 = 12.5% TB Tb TB Tb tB tb ttBB = 1/16 = 6.25% Ttbb = 2/16 = 12.5% tB tb TB TTBB TTBb TtBB TtBb TtBb = 4/16 = 25% TtBB = 2/16 =12.5% Tb TTBb TTbb TtBb Ttbb TTbb = 1/16 = 6.25% TB TTBb = 2/16 = 12.5% TTBB = 1/16 = 6.25% Tb tB TtBB TtBb ttBB ttBb Phenotype Tall, blue = 9/16 (56.25%) Short, blue = 3/16 (18.75%) Tall, white = 3/16 (18.75%) Short, white = 1/16 (6.25%) tB tb TtBb Ttbb ttBb ttbb tb

54 Incomplete dominance & Codominance
When a mouse with black fur is crossed with a mouse with white fur, all F1 generation offspring have gray fur. What are the probable genotypes and phenotypes for the F2 generation? Is this an example of codominance or incomplete dominance? What would the possible genotypes and phenotypes be for a cross between a roan-coated cow (CR CW) and a red-coated cow (CR CR)? Is this an example of codominance or incomplete dominance?

55 Blood Type Problems A couple preparing for marriage have their blood typed. They are both AB. They are curious about the possible blood types their children might have. What are the possible phenotypes of their children? A type A person marries a type A person. Their firstborn has type O blood. What are the genotypes of the parents and the child? A wealthy elderly couple die together in an accident. Soon a man shows up to claim their fortune, claiming he is their long lost son. Other relatives dispute the claim. Hospital records show that the deceased couple were blood types AB and O. The person claiming to be their son is type O. Do you think this man is an impostor? Explain why.


Download ppt "Unit 3 Genetics."