Please keep all extra notes and practice problems neatly organized in your notebook so that may reference them as needed This information is covered in 6.3, 6.4, 6.5 and chapter 7 of your textbook
Study of biological patterns and in organisms are distinguishing characteristics that are inherited Give some examples of traits
Portion of DNA that codes for a protein Different variations of the same gene Two copies of the same allele (one copy inherited from each parent). Term should be paired with either dominant or recessive Two different alleles of the same gene (one copy inherited from each parent) An allele that is expressed when at least one copy is present (represented by upper case letters) Alleles that are only expressed when there are two copies are present (represented by lower case letters) Genetic make up of a gene (use words like hetero/homozygous and dom/recessive to describe genotype) Physical characteristics (think height color, size, shape, disorder/no disorder etc)
AA: Aa: Aa: A: a: are variations of the same The guinea pig has white fur: White fur is the result of a homozygous recessive.
Remember, if you have the dominant phenotype, you can t be sure about your genotype without more information. You might be homozygous dominant or heterozygous as both of these genotypes result in a dominant phenotype.
Father of Experimented on (homozygous) pea plants, which produce either white or purple flowers and have many other simple, either/or traits
Mendel consistently received the same results when crossing ( ) a purebred white plant with a purebred purple plant P for parent, F1 first filial, F2 second filial
Law of segregation Allele pairs segregate (separate) during (meiosis) Half of the resulting gametes will carry one allele while the other half will carry the other Law of Independent Assortment Allele pairs separate independently during gamete formation (that is, traits are inherited separately and the alleles that appear on one chromosome will have no influence on the alleles that appear on another)
Examine the inheritance probabilities for one trait using 2x2 Punnett squares 1. What would be the genotype of parent 1? Parent 2? 2. Would these parents express the dominant or recessive phenotype? 3. What are the chances that these parents will produce a child with the dominant phenotype? Recessive? 4. What are the chances that these parents will produce a child with a homozygous dominant genotype? Heterozygous? Homozygous recessive?
Answer questions 1-9 on the Punnett Square Practice sheet. Do not attempt number 10 yet.
Used to determine the of an organism expressing the phenotype This is done by crossing the with an organism expressing the recessive phenotype (as the genotype of such an organism be homozygous recessive).
Testcross quick lab. Page 185 in textbook
Examine the inheritance probabilities for two traits using 4x4 Punnett squares. Let s use an example: Start by writing the genotypes for mom: and dad:
Now to put this into a 4x4 Punnett square...
Once you ve figured out all the possibilities for the eggs and sperm, it s easy to fill in the chart. Just make sure each offspring has TWO alleles for BOTH genes (no Hhhh or RRrr). From here, I could ask the same type of probability questions that I do for monohybrid crosses. You could do it, but you d quickly realize that it requires A LOT more work and who likes more work? Especially when it s not necessary
For an oompa mom that is homozygous recessive for hand color and tongue rolling (hhrr) and an oompa dad that is heterzygous for both (HrRr), describe the probability that they will produce the following offspring: 1. Orange-handed tongue roller 2. Pale-handed tongue roller 3. Orange-handed non roller You could draw a 4x4 Punnett square and count, but multiplying the probability of inheriting each trait separately is easier and faster Here s how to approach #5: 4. Pale-handed non roller 5. Hhrr genotype 6. hhrr genotype Here s how to approach number 1: You try #6 You try #2, 3 and 4
You should have found all the probabilities (1/4 th 25%) to be the same based on the parent genotypes. Let s try one that s less predictable. Black fur (B) is dominant to white fur (b) in guinea pigs Curly hair (H) is dominant to straight hair (h) Consider a cross of two guinea pigs that are both heterozygous for both traits and answer the following questions: What s the probability of babies with curly, black fur? Straight, black fur? Curly, white fur? Straight, white fur? What s the probability of babies with a BBHH genotype? BbHh? bbhh? BBHh? bbhh? BbHh? bbhh? BBhh?
So far, we have learned about traits that are carried on autosomal traits/diseases These traits affect all genders equally Traits can also be carried on Called sex-linked traits or diseases Since, X is far larger than Y, it carries far more genes So sometimes sex-linked is simply called X-linked because Y-linked traits and diseases are very rare.
Because males carry X chromosome, they will automatically express all alleles carried on it, recessive or dominant Females have two X chromosomes so they will only express a recessive allele if they have two copies Examples: How to set up a sex-linked punnett square for Color blindness and Hemophilia
Most diseases are carried on a the recessive allele Meaning you must inherit to be affected Some diseases are carried on the allele Dangerous because homozygous dominant and heterozygous individuals are affected Example: Huntington's disease
Summarize potential offspring 1. Hippo syndrome (H/h) is an autosomal recessive disorder. Cross two heterozygotes. 2. Laidback syndrome(b/b) is an autosomal dominant disorder. Cross two heterozygotes. 3. Grumpy disorder (G/g) is an x-linked recessive disorder. Cross a mother that is a carrier with a father that has grumpy disorder.
In female mammals, one X chromosome is randomly "turned off. That way, both males and females have only one functional X chromosome. In calico cats the result of X-inactivation is apparent in the color of their fur because the genes for orange and black fur are carried on the X chromosome Ms. D s Cat, Jojo Jojo
When the heterozygote exhibits a phenotype that is somewhere the two homozygous phenotypes (instead of fully exhibiting the dominant phenotype). In the snapdragon flower, heterozygote are pink Practice incomplete dominance by completing #10 on your punnett square practice sheet.
When one trait is not dominant over the other. The heterozygote will express both homozygous phenotypes. Blood type is an example of a codominant trait. uses the letter I/I O blood is homozygous recessive, ii A and B are BOTH dominant so you always have be clear which dominant allele you are referring to I A or I B this means you should never write a capital I with no superscript next to it.
1. The father is type A heterozygous, the mother is type B heterozygous. Describe the phenotypic and genotypic possibilities for their offspring. 2. The father is type A homozygous, the mother is type B homozygous. 3. Both the father and mother have type AB blood. Describe the phenotypic and genotypic possibilities for their offspring. 4. Alice has type A blood and her husband Mark has type B blood. Their first child, Amanda, has type O blood. Their second child, Alex, has type AB blood. What is Alice s genotype? What is Mark s genotype? (draw a Punnett square that confirms your answer 5. Candace has type B blood. Her husband Dan has type AB blood. Is it possible for Candace and Dan to have a child that has O blood? Explain why or why not (use a Punnett square to help). 6. Ralph has type B blood and his wife Rachel has type A blood. They are very shocked to hear that their baby has type O blood, and think that a switch might have been made at the hospital. Can this baby be theirs? Explain why or why not (use a Punnett square to help).
Traits that are influenced by genes that may or may not occur on the same chromosome A simple Punnett square be used to predict these traits These traits often have a range of phenotypes instead of this or that. examples: human height (at least 3 genes involved), eye color (at least three genes), and skin color (about twelve genes). Fraterenal twin girls with biracial parents Some phenotypes, like skin color, can be influenced by the environment (tanning)
Genes that are to one another on a chromosome (so close the are unlikely to separated during meiosis) are considered liked. can be used to display the distance between genes, which can sometimes help explain certain inheritance patterns If two genes are one apart, that means that they cross over 1% of the time. These genes would be considered linked. Ex: Draw a linkage map based on the following cross over percentages for three gene pairs: A-B = 8%, B-C =10%, A-C = 2% Tip draw the the gene pairs that are farthest apart first Kind of like this: B C (you could use centimeters on a ruler to be more exact) Note that A should be 8 maps unit from B, but also 2 units from C. They only possible placement for A in between B and C Kind of like this: B A C Now you try: A-D= 40%, A-B=10%, B-C=40%, C-A= 50%, B-D=30%, C-D=10% Try another: A-D=12.5%, B-C=50%, C-D=25%, B-D=25%, A-C=12.5%, E-B=10%, E-C=60%
Determine the pattern of inheritance Circle = female Square = male Shaded = expresses trait/disorder Horizontal line = marriage/couple Vertical line = children of couple directly above X-linked dominant? X-linked recessive? Autosomal dominant? Autosomal recessive?
Determine the pattern of inheritance X-linked dominant? X-linked recessive? Autosomal dominant? Autosomal recessive?
A picture of all the chromosomes in a cell Can be used to identify chromosomal disorders