1. Chapter 7: Genes and Inheritance
Family resemblance: how traits are inherited

3. In many cases, the answers to questions about heredity are simple
In many cases, the answers to questions about heredity are simple. Fish odor syndrome, for example, is just such a case. Recall from Chapter 6, that sexually reproducing organisms generally carry two copies of every chromosome in every cell, because they inherit one copy of each chromosome from each parent.
At each location on the two chromosomes of a pair is the same gene; one copy from the mother and one from the father. The gene for FMO3 is on chromosome #1. There is a normal version of the gene for FMO3, which most people carry, and there is a rare and defective version that is responsible for fish odor syndrome. As long as a person has at least one normal version of the FMO3 gene, he or she will produce enough of the enzyme to break down the fishy chemical. But if a person inherits two copies of the defective version of the fish-odor gene, one from each parent, that person will inherit the disorder.
In this chapter we explore how heredity works. We’ll also examine why the behavior of some traits is easy to predict while many other traits have less straightforward patterns of inheritance.
Figure 7-3 Unlucky catch.

4. Selective Breeding: by observing heredity
Breeding animals for ages
Even though there was no knowledge about the transmission of traits from parents to offsprings.
Race Horse Breeding
Observing heredity is easy. Elucidating how it works is not.
For thousands of years before the mechanisms of heredity were discovered and understood, plant and animal breeders understood that there is a connection from parents to offspring across generations. This recognition was enough to enable them to systematically create strains of crops, livestock, and even pets with desirable traits (Figure 7-5).
Once breeders recognized the existence of heredity, they began selecting those individuals with the desired traits to breed with each other, in the hope that their offspring would have the desirable trait.

5. PLANT BREEDING Green revolution Norman Borlaug : Nobel peace prize
High yielding wheat and rice varieties
Norman Borlaug : Nobel peace prize

6. Gregor Mendel (Mid 1800s) Father of Genetics
a monk
an agronomist
a mathematician
Didn’t know about
DNA, genes
Chromosomes
meiosis
Petal
Carpel
Stamen

7. Existing theories during Mendel’s time..….
Pre-made Humans???
Blending theory???

8. Why did Mendel use pea plants?
short life cycles
easy to maintain
Easy to breed
Several traits which were easily distinguishable
Short life cycle (quick reproduction time)
Easy to breed (fertilization easily controlled)

9. Mendel’s success (was because of hard work and luck)
Choice of ideal organism
Established true breeding populations
Choice of traits which occurred only in ____ versions
Traits controlled by ___ gene
H elooked at 7 traits and it turns out there are 7 chromosomes in pea plant and each of those genes were on the separate 7 chromosomes

10. DOMINANT TRAITS RECESSIVE TRAITS Freckles Widow’s peak Free earlobe
Human traits determined by a single gene
DOMINANT TRAITS
Freckles
Widow’s peak
Free earlobe
Figure 9.12 Examples of inherited traits thought to be controlled by a single gene.
RECESSIVE TRAITS
No freckles
Straight hairline
Attached earlobe

11. Alleles – alternate forms of a gene
Homologous chromosomes have the same genes but can have different ______
Allele - an alternate form of a gene.
Ex. stem length gene has 2 alleles - tall allele & short allele
Dominant allele - allele that masks the expression of another allele.
Ex. tall allele (T)
Recessive allele - allele whose expression is masked by another allele.
Ex. short allele (t)
Trait: Stem length
Alleles: Tall allele (T) Short allele (t)

12. How many copies of each gene do you have?
A. One copy B. Two copies C. Twenty three copies D. Differs from person to person
Ans: B

13. Dominant and Recessive traits
2 dominant alleles for gene ‘A’
AA: homozygous dominant
1 dominant & 1 recessive allele for gene ‘B’
Bb: heterozygous dominant
A diploid cell has two alleles for every gene located on a homologous pair of chromosomes. [one allele from each of the organism’s parents]
2 recessive alleles for gene ‘D’
dd: homozygous recessive

14. Check out your neighbor’s earlobes. Are they attached or free?
Free (Dominant)
Attached(Recessive)

15. The letter F represents the earlobe allele
The letter F represents the earlobe allele. If your neighbors earlobes are attached, and this trait is recessive, what alleles did they inherit?
A. Ff
B. FF
C. ff
D. ffF
Ans: C

16. Some genetics vocabulary
Phenotype: the outward appearance of an individual
Free or Attached
Genotype: the individual’s genetic composition
FF (homozygous dominant)
ff (homozygous recessive)
Ff (heterozygous dominant)

17. Writing genotypes for Cystic Fibrosis

18. Dominant and Recessive traits
The blue arrows point to a pair of alleles that are ____
Homozygous dominant
Heterozygous dominant
Homozygous recessive
Recessive
Ans: B
A diploid cell has two alleles for every gene located on a homologous pair of chromosomes. [one allele from each of the organism’s parents]

19. Brain Storm….
If some traits are single gene and recessive (like fish odor syndrome), shouldn’t there be fewer people in a population that have the recessive gene?
Dominant traits are not necessarily normal or more common

20. A dominant trait masks the effect of a recessive trait.
Mendel’s monohybrid experiment with pea plants looking at a single trait (like flower color), lead to Law of segregation
A dominant trait masks the effect of a recessive trait.
Here’s where Mendel’s meticulous and methodical experiments paid off. First, he started with true-breeding white-flowered plants. Then he got some true-breeding purple-flowered plants. He wondered: which color wins out when the white-flowered plant is crossed with the purple-flowered plant? The answer was definitive: purple wins. All of the offspring were purple, every time. For this reason, Mendel called the purple-flower color trait dominant, and he considered the white-flower color trait to be the recessive trait. In general, a dominant trait masks the effect of a recessive trait when the individual carries both the dominant and the recessive versions of the instructions for the trait. (Figure 7-9)
Mendel’s law of segregation describes the inheritance of a single characteristic
From his experimental data
Mendel deduced that an organism has two genes (alleles) for each inherited characteristic

21. Law of _________: you’ve got two copies of each gene but ____ helps put only ____ copy in each sperm or egg.
Things got a bit more interesting when Mendel took the purple-flowered plants that came from the cross of purple- with white-flowered plants and bred them with each other. He found that these mixed-parentage plants were no longer true-breeding. Occasionally, they would produce white-flowered offspring. Apparently, the directions for building white-flowers—last seen in their grandparents—were still lurking inside the purple-flowered plants. The existence of traits that could disappear for a generation and then show up again was quite perplexing. Mendel devised a simple and perfect hypothesis to explain these observations (Figure 7-10).

22. Three Ideas Mendel Used for Explaining This Pattern of Inheritance
Each parent puts into every sperm or egg it makes a single set of instructions for building the trait.
Offspring receive two copies of the instructions for any trait (called alleles).
The actual trait observed in an individual depends on the two copies of the gene that they inherit from their parents.
Homozygous and heterozygous

23. How do we determine what traits offsprings inherit?
Answer: By doing _______ _____
To do punnett square you need to know
Genotypes
Type of gametes made
Then do the punnett square

24. Dimples
No dimples
Genotype Dd dd

25. offspring genotype possibilities
genetic contribution
of one parent
dimples D d
genetic contribution
of one parent
offspring
genotype
possibilities d D d d d
no dimples d D d d d 25

26. What is the chance that a man homozygous for dimples and woman with no dimples will have a kid with dimples (No dimples is a recessive trait)
25%
50%
75%
100%
Ans: d

27. Mendels dihybrid experiments looking at two traits in a plant (like flower color and seed shape) resulted in Law of independent assortment
7.16 Most traits are passed on as independent features: Mendel’s law of independent assortment.
Sometimes you can be right about something for the wrong reason. This happened to Gregor Mendel. He didn’t know that genes were carried on chromosomes, so he believed that they were all just free-floating entities within cells. Given this perspective, it made sense to him that the inheritance pattern of one trait wouldn’t influence the inheritance of any other trait. He believed all genes behaved independently. 27

28. Imagine that you had a true-breeding population of cats with white fur
Imagine that you had a true-breeding population of cats with white fur. Now suppose that an individual in this population mated with a cat from a true-breeding population of cats that all had some colored fur (all individuals have the genotype ww). All of their offspring would have white fur, but they would be heterozygous (Ww), getting a dominant allele from their white-furred parent and a recessive allele from the other parent. If two heterozygotes had offspring together, though, they would produce three-quarters white-furred and one-quarter non white-furred offspring, with genotypes in the ratio of 1⁄ 4W W, 1⁄ 2 Ww, and 1⁄ 4 ww. That is just what Mendel observed for traits in pea plants.
But what if we concurrently observed another characteristic of these cats? Suppose the original true-breeding population of white-furred cats (WW) was also true-breeding for long hair (all ll), a condition caused by carrying two recessive alleles for a single gene. And suppose that individuals in the colored-fur population (ww) were also true-breeding for short hair (all LL). The question is, do the alleles an individual inherits for the white-fur trait influence which alleles that individual inherits for fur length? And the answer is that they do not (Figure 7-28). Rather, the first cross of a long-haired, all-white cat with a cat having short, colored fur would result in offspring heterozygous for both traits—referred to as dihybrid—and expressing each of the dominant traits. 28

29. What are the type of gametes made from an organism with genotype LlWw?
FOIL method LW Lw lW lw
Traits are inherited independent of each other
Law of Independent Assortment:
each pair of alleles ( Ll or Ww) segregates independently during gamete formation

30. In the test-cross, you take an individual exhibiting a dominant trait but whose genotype is unknown. You cross (i.e., mate) that individual with an individual that is homozygous recessive and look at the phenotypes of the offspring. There are two possible outcomes, and they reveal the genotype of your unknown-genotype alligator. If your alligator is homozygous dominant (MM), it will contribute a dominant allele, M, to every offspring. Even though the albino alligators will contribute the recessive allele, m, to all its offspring, the offspring will all be heterozygous, Mm, and none of them will ever be white.
If, on the other hand, your unknown-genotype alligator is heterozygous, Mm, half of the time it will contribute a recessive allele, m, to the offspring. In every one of those cases, the offspring will be white and homozygous recessive. So the cleverness of the test-cross is that when you cross your unknown genotype organism with an individual showing the recessive trait, if it sometimes—half the time, on average—produces offspring with the recessive trait its genotype must be heterozygous. If it never produces offspring with the recessive trait it must be homozygous for the dominant allele. 30

31. A. You could get gametes with RrYY
You have a pea plant that is heterozygous for pea shape and homozygous dominant for pea color, RrYY. Which of the following are possible allele combinations that you could see in the sex cells from your plant?
A. You could get gametes with RrYY
B. You could get gametes with Rr or YY
C. You could get gametes with RY or rY
D. You could get gametes with R or r or Y
Ans: C

32. If you are heterozygous for earlobe attachment, what percentage of your gametes will have the “F” gene?
25%
50%
75%
100%
Ans: B