1. Unit 8: Genetics & Heredity Unit 9: Human Genetic Disorders Ch
Unit 8: Genetics & Heredity Unit 9: Human Genetic Disorders Ch. 26: Inheritance of Traits & Ch. 27: Human Genetics

2. Unit 8: Genetics & Heredity
What is genetics?
the study of heredity
passing of traits from parents to offspring
Genetics is the study of heredity. Heredity the passing of traits from parents to offspring

3. Chromosomes in Cells Remember… body cells are diploid
2 of each chromosome
1 from mom & 1 from dad
gametes (sperm & eggs) are haploid
1 of each chromosome
Why?
So zygote gets right # of chromosomes…
Why? So that when fertilization occurs the zygote has the correct # of chromosomes… if gametes were diploid then the zygote would have double the correct # of chromosomes

4. Genes Why is your combination of genes unique?
Chance… don’t know which sperm will fertilize which egg…
get ½ of your chromosomes from mom & ½ from dad
meiosis (formation of gametes)
crossing-over during prophase 1
alignment of chromosomes during metaphase 1
Genetics is the study of heredity. Heredity the passing of traits from parents to offspring
Why is your combination of genes/traits unique? ½ your genes (on chromosomes) came from your mom, ½ from your dad! But – you also have your own unique gene combination! b/c when the egg and sperm that became your first cell were formed during meiosis, crossing over & independent assortment mixed up your genes, giving you a one-of-a-kind genotype…unless you are an identical twin! This genetic recombination, all based on chance, is what gives all living things variation, and this is what drives the process of evolution.

5. Genes & Alleles What is a “gene”?
section of chromosome that codes for a specific protein
& determines a specific trait (ex. hair color, eye color, ear shape, etc.)
genes are paired on homologous chromosomes
different forms of genes for the same trait are called “alleles”
Organisms have thousands of different traits.
Each chromosome has different kinds of genes that control different traits…
Remember… chromosomes in body cells are paired (homologous)… so, the genes on chromosomes are paired too….
Different forms of genes for the same trait are called alleles

6. Dominant & Recessive Alleles
Each parent contributes 1 allele (form of gene) for trait & can be dominant or recessive
What is a dominant allele?
allele that prevents expression of (“masks”/“hides”) recessive trait
What is a recessive allele?
allele whose trait can be seen only when the organism is pure (homozygous) for that trait
Different forms of genes for the same trait are called alleles
Dominant  “speaks for both alleles”
for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype (2 copies of recessive allele)
Use same letter to represent dominant & recessive… dominant shown by CAPITAL & recessive shown by lowercase

7. Dominant & Recessive Alleles
How are alleles represented?
with letters
usually the first letter of the dominant trait
If the same letter is used for dominant & recessive, how do we know which allele is which?
CAPITAL = DOMINANT
lowercase = recessive
Different forms of genes for the same trait are called alleles
Dominant  “speaks for both alleles”
for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype (2 copies of recessive allele)
Use same letter to represent dominant & recessive… dominant shown by CAPITAL & recessive shown by lowercase

8. Allele Combinations What does “homozygous” mean?
both alleles are the same
homozygous (pure) dominant (ex. AA)
homozygous (pure) recessive (ex. aa)
What does “heterozygous” mean?
both alleles are different
heterozygous (hybrid) (ex. Aa)
Different forms of genes for the same trait are called alleles
Homozygous  inherited two identical forms (or alleles) of the gene
can be homozygous dominant
can be homozygous recessive… This is the ONLY way for the recessive trait to be expressed
Heterozygous  inherited two different forms (or alleles) of the gene
dominant allele is always expressed; recessive allele is “hidden” by dominant allele

9. Genotype vs. Phenotype What is “genotype”? What does the genotype do?
organism’s actual genetic “code”/make-up (alleles)
What does the genotype do?
codes for protein that causes trait (phenotype)
How do we represent an organism’s genotype?
2 letters (one for each allele)
one from mom & one from dad
ex. PP, Pp, pp
Genotype: Collection of alleles (genes) Represented by capital letters for dominant alleles, and lowercase letters for recessive alleles
Two alleles/genes/letters for each trait
Phenotype: Collection of proteins; expressed in traits (form and function) Traits may be dominant or recessive, because they are coded for by dominant or recessive alleles
for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype

10. Genotype vs. Phenotype What is “phenotype”?
the outward (physical) expression of the genotype (trait we “see”)
What actually causes the “phenotype” (trait) we see?
the protein that is produced (due to the organism’s genotype “code”/alleles)
How do we represent an organism’s phenotype?
usually an adjective
ex. purple, white, tall, short, etc.
Genotype: Collection of alleles (genes) Represented by capital letters for dominant alleles, and lowercase letters for recessive alleles
Two alleles/genes/letters for each trait
Phenotype: Collection of proteins; expressed in traits (form and function) Traits may be dominant or recessive, because they are coded for by dominant or recessive alleles
for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype

11. Genotype is Expressed as a Phenotype
Ex. Let P = purple & p = white
homozygous (pure) dominant
genotype PP
phenotype = purple
homozygous (pure) recessive
genotype pp
phenotype = white
heterozygous (hybrid)
genotype Pp
dominant trait “masks/hides” recessive trait
Genotype: Collection of alleles (genes) Represented by capital letters for dominant alleles, and lowercase letters for recessive alleles
Two alleles/genes/letters for each trait
Phenotype: Collection of proteins; expressed in traits (form and function) Traits may be dominant or recessive, because they are coded for by dominant or recessive alleles
for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype

12. PP Pp pp
genotype = actual genetic make-up of individual (alleles) codes for phenotype (trait) represented by 2 letters
1 to represent gene from mom & 1 from dad ex. PP, Pp, pp
phenotype = outward (physical) expression of the genotype trait we “see” (due to) the protein that is produced
usually represented by an adjective ex. purple, white, etc.
for recessive phenotype (trait) to be expressed, must have homozygous recessive genotype

13. Predicting Traits in Offspring
What are Punnett Squares?
a way to predict the results of crosses (mating)
letters outside represent possible alleles in gametes of each parent
top = one parent & side = other parent
letters inside boxes represent possible allele combinations (genotypes) in offspring (& phenotypes)
can be used to determine probability and ratios BB Bb
1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a Punnett square 4. "split" the letters of the genotype for each parent & put them "outside" the Punnett square (one on left & one on top) to represent the possible alleles in the gametes
5. determine the possible genotypes of the offspring by filling in the Punnett square 6. summarize results (genotypes & phenotypes of offspring)
Parent Pea Plants ("P" Generation) Genotypes: Tt x tt Phenotypes: tall x short Offspring ("F1" Generation) Genotypes: 50% (2/4) Tt & 50% (2/4) tt
Phenotypes: 50% tall & 50% short

14. Making a Punnett Square
Parents are Tt & tt genotypes…
So… Tt x tt is our cross (mating)
1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a Punnett square 4. "split" the letters of the genotype for each parent & put them "outside" the Punnett square (one on left & one on top) to represent the possible alleles in the gametes
5. determine the possible genotypes of the offspring by filling in the Punnett square 6. summarize results (genotypes & phenotypes of offspring)
Parent Pea Plants ("P" Generation) Genotypes: Tt x tt Phenotypes: tall x short Offspring ("F1" Generation) Genotypes: 50% (2/4) Tt & 50% (2/4) tt
Phenotypes: 50% tall & 50% short

15. Passing Traits to Offspring & Probability
What is probability?
chance an event will occur
What is the chance of getting heads? tails?
If you flip two coins, of getting 2 heads? 2 tails?
½ x ½ = 1/4
What is the chance of a couple having a boy? a girl?
1/2
of having five girls?
½ x ½ x ½ x ½ x ½ = 1/32
or ( ½ )5 = 1/32

16. Passing Traits to Offspring & Ratios
What is a “genotypic ratio”?
probable ratio of genotypes (alleles) in offspring of a given cross
Ex. If cross Pp & Pp
1PP : 2Pp : 1 pp
Expected & observed ratio can differ b/c it is possible (although less probable) that 4 offspring with the same traits…. The larger the # of offspring, the more likely the 2 ratios will be closer…
 The phenotype ratio in a monohybrid cross is never exactly 3:1.
This is because of the random nature of fertilization and the fact that some embryos die during early stages.

17. Passing Traits to Offspring & Ratios
What is a “phenotypic ratio”?
probable ratio of phenotypes (traits) in offspring of a given cross
resulting from the genotypes of the offspring
Ex. If cross Pp & Pp
3 purple : 1 white

18. Passing Traits to Offspring & Ratios
What is an “expected ratio”?
ratio we expect to get based on probability (Punnett Square)
What is an “observed ratio”?
ratio we actually get
Why would these be different?
fertilization is random
some embryos die during early stages
Expected & observed ratio can differ b/c it is possible (although less probable) that 4 offspring with the same traits…. The larger the # of offspring, the more likely the 2 ratios will be closer…
 The phenotype ratio in a monohybrid cross is never exactly 3:1.
This is because of the random nature of fertilization and the fact that some embryos die during early stages.

19. Gregor Mendel Father of Genetics studied garden pea plants 1822-1884
7 different traits with clearly different forms
tried to determine how they were passed from parent to offspring
Austrian monk did his work around 1865….
Used peas b/c reproduce much more quickly and could use many plants at once

20. Mendel’s Experiments
What happened when Mendel mated a pure purple parent (PP) & a pure white parent (pp)?
all offspring had:
purple phenotype
heterozygous (hybrid) genotype Pp
Noticed purple flowered-plants mated with white-flowered plants always resulted in purple-flowered offspring

21. Mendel’s Experiments
What happened when Mendel let the heterozygous (hybrid) offspring from his first experiment self-pollinate?
So… Pp x Pp
new offspring weren’t all purple…
all (F1) offspring (of pure purple w/ pure white parents) should have Pp genotype …. & should produce ½ their gametes w/ P gene & ½ w/ p gene…
So if cross two (F1) first generation offspring (Pp x Pp) there will be 3 possible combinations for 2nd generation offspring…. PP, Pp (x2), and pp w/ a 3:1 phenotypic ratio expected….

22. Mendel’s Principle of Dominance
What did Mendel notice from his experiments?
that one form dominates over the other
…dominant trait prevents the expression of the recessive trait
What trait was dominant in these plants?
PUPRLE = dominant
What trait was recessive?
white = recessive
Genes (Mendel called them “factors”) come in pairs – one from the egg and one from the sperm. Each gene of a pair is called an allele. An allele may be either dominant, which means only one copy of the allele is needed in the organism’s genotype for its protein product to be expressed in the phenotype, or it may be recessive, in which case two copies of the allele need to be present in the genotype for its protein product to be expressed in the phenotype.
Principle of dominance When an organism has two different alleles for a trait, the allele that is expressed, overshadowing the expression of the other allele, is said to be dominant. The gene whose expression is overshadowed is said to be recessive

23. Dominant/Recessive is Not Always the Method of Inheritance
Traits are not always as clearly defined as the 7 pea plant traits Mendel studied.
examples of non-dominant/recessive inheritance
sex determination
sex-linked traits
codominance
multiple alleles
Called non-Mendelian modes of inheritance

24. Sex Determination How many chromosomes do humans have (in body cells)?
46… 23 pairs
pairs 1 – 22 = autosomes (body chromosomes)
23rd pair determines gender = sex chromosomes
XX = female
XY = male
Which parent’s chromosomes determines if the offspring will be a boy or girl???? Why?
Dad’s b/c he is the only one that can give a Y; mom always gives X.
What is the probability of having a son? A daughter?
Which parent’s chromosomes determines if the offspring will be a boy or girl???? Father b/c mother always contributes X chromosome… if dad contributes X  girl… if dad contributes Y chromosome  son
So…. Blame dad if you didn’t get the little brother/sister you wanted….

25. Sex-linked Inheritance
X & Y chromosomes not fully homologous. Why?
X is bigger & carries more genes
X-linked traits & disorders more common in males Why??? b/c female has XX, more likely she will have a copy of dominant allele… males XY… can only get dominant allele on X
Hemophilia is a group of bleeding disorders in which it takes a long time for the blood to clot.

26. Sex-linked Inheritance
How many alleles will a male have for traits carried only on the X chromosome?
1 b/c only have 1 X chromosome (Y doesn’t have allele)
What is this called?
X-linked or sex-linked
Ex. eye color in fruit flies, hemophilia in humans, colorblindness in humans
X-linked traits & disorders are more common in males. Why???
b/c female has XX, more likely she will have a copy of dominant allele… males = XY… can only get dominant allele on X (& only have 1 X)
X-linked traits & disorders more common in males Why??? b/c female has XX, more likely she will have a copy of dominant allele… males XY… can only get dominant allele on X
Hemophilia is a group of bleeding disorders in which it takes a long time for the blood to clot.

27. Sex-linked Inheritance
How do we make predictions made using Punnett squares for sex-linked traits?
Consider the sex chromosome (X/Y) & allele for the trait it carries (“exponent”) TOGETHER as a unit…
ex. XG (= X w/ dominant allele), Xg (= X w/ recessive allele), Y (= Y w/ NO allele)
What if a female is heterozygous (XGXg)?
she does not show the
trait/have the disorder,
but is a carrier
& can pass gene
to offspring
Can a male be a carrier?
No, b/c only has one X chromosome w/ allele… so either has it or doesn’t
XG Xg
XG XG XG Xg
XG Y Xg Y XG Y

28. Sex-linked Inheritance
Drosophila (fruit fly) eye color is sex-linked
What are the sex, genotype, & phenotype of each offspring? Are there any carriers for the white eye gene?
Left picture: 2 females with red eyes = XRXr (carrier white eye gene) & 2 males with white eyes = XrY
Right picture: female w/ red eyes = XRXR, female w/ red eyes = XRXr (carrier white eye gene), male w/ red eyes = XRY, & male w/ white eyes = XrY
XR Y
Make sure students know symbols for male & female… Male… arrows… hunting… female… arms… gathering (or hugging)
What are the sex, genotype, & phenotype of each offspring?
left picture  2 females with XRXr red eyes (carrier for white eye gene) 2 males with XrY white eyes
right picture  Female XRXR red eyes Female XRXr red eyes (carrier for white eye gene) Male XRY red eyes Male XrY white eyes
XR XR XR Y
XR Xr Xr Y XR Xr

29. Multiple Alleles & Codominance
What is meant by multiple alleles?
more than 2 different forms of an allele exist
but individual still has just 2
Ex. human blood types
(3) multiple alleles
A (IA)
B (IB)
o (i)
How many possible genotypes are there?
How many phenotypes?
Can you spot the blood type that is the result of codominance?
How many possible genotypes are there? (AA, AO, BB, BO, AB, O)
How many phenotypes? 4 (A, B, AB, O)
Can you spot the blood type that is a product of codominance? AB

30. Multiple Alleles & Codominance
What is meant by codominance?
both alleles are “expressed” equally
Ex. human blood types also exhibit codominance (as well as multiple alleles)
A & B are codominant and are “expressed” equally
A = B (codominant)
o (recessive)
So… (A = B) > o
How many possible genotypes are there?
How many phenotypes?
How many possible genotypes are there? (AA, AO, BB, BO, AB, O)
How many phenotypes? 4 (A, B, AB, O)
Can you spot the blood type that is a product of codominance? AB

31. Unit 9: Human Genetic Disorders
What causes genetic disorders?
DNA mutation (usually recessive) or chromosome abnormalities (in # or structure) that cause the production of abnormal proteins

32. Human Genetic Disorders
How can we group genetic disorders?
autosomal recessive disorders (*most genetic disorders)
allele is recessive & found on a chromosome from pairs 1 – 22 (autosomes or body chromosomes)
cystic fibrosis, sickle-cell anemia, Tay-Sachs disease
autosomal dominant disorders
allele is dominant & found on a chromosome from pairs 1 – 22 (autosomes or body chromosomes)
Huntington’s Disease
sex-linked disorders
allele (which is usually recessive) is found on the 23rd pair of chromosomes (sex chromosomes)… Usually on the X chromosome
hemophilia, color blindness
chromosomal abnormality disorders
result from errors in chromosome # or structure
Down Syndrome (trisomy 21), Klinefelter’s Syndrome (XXY)

33. Autosomal Recessive Disorders
What genotype(s) must a person have to be affected?
homozygous recessive (gg)
cystic fibrosis
sickle-cell anemia
Tay-Sachs Disease
Can someone be a carrier? Why/why not?
yes
b/c if heterozygous (Gg), person carries the gene, but isn’t affected
due to having the “normal” dominant gene
in all of these examples
Do the parents have the disorder? No (both ARE carriers)
If they only had one child, what would the chance be for that child to be affected by the disorder? ¼ or 25%
What is the probability that the child would be a carrier? 2/4 or ½ or 50%
autosomal recessive disorders (*most genetic disorders)
allele is recessive & found on a chromosome from pairs 1 – 22 (autosomes or body chromosomes)
cystic fibrosis, sickle-cell anemia, Tay-Sachs disease

34. Autosomal Dominant Disorders
What genotype(s) must a person have to be affected?
can be homozygous (GG) or heterozygous (Gg) b/c allele is dominant
Huntington’s Disease
Can someone be a carrier? Why/why not? No
b/c even if person is heterozygous (Gg), person will have disorder
due to dominant “disease” gene blocking “normal” recessive gene
autosomal dominant disorders
Allele is dominant & found on a chromosome from pairs 1 – 22 (autosomes or body chromosomes)
Huntington’s Disease

35. Sex-linked Disorders
Remember from earlier… hemophilia is X-linked & recessive
What are the possible genotypes & phenotypes? Can someone be a carrier?
XHXH = normal female
XHXh = carrier female (but not affected)
XhXh = female w/ hemophilia
XHY = normal male
XhY = male w/ hemophilia
Why can’t a male be a carrier?
b/c only has one X chromosome w/ allele… so either has it or doesn’t
Ex. mom = carrier & dad = normal:
Make a Punnett square.
genotypic ratio?
phenotypic ratio?
P. Sq.: Mother carrier & father normal
Genotypic ratio 1 XHXH : 1 XHXh : 0 XhXh: 1 XHY : 1 XhY
Phenotypic ratio: 1 normal female : 1 female carrier : 0 female w/ hemophilia: 1 normal male : 1 hemophiliac male
sex-linked disorders
allele (which is usually recessive) is found on the 23rd pair of chromosomes (sex chromosomes)… Usually on the X chromosome
hemophilia
color blindness
1 XHXH: 1 XHXh: 0 XhXh: 1 XHY: 1 XhY
1 normal female: 1 carrier female : 0 female w/ hemophilia: 1 normal male: 1 hemophiliac male

36. Sex-linked Disorders
Remember from earlier… colorblindness is X-linked recessive
What are the possible genotypes & phenotypes? Can someone be a carrier?
XCXC = normal female
XCXc = carrier female (but not affected)
XcXc = colorblind female
XCY = normal male
XcY = colorblind male
In this Punnett square, what are the genotypes & phenotypes of the parents?
father:
genotype = XCY & phenotype = normal
mother:
genotype = XCXc & phenotype = carrier
Ishihara
test for
red-
green
color-
blindness
In this Punnett square, what are the genotypes & phenotypes of the parents?
Father: genotype = XCY phenotype = normal mother: genotype = XCXc phenotype = carrier for color blindness
Color blindness is the inability to see certain colors in the usual way.
Color blindness occurs when there is a problem with the color-sensing materials (pigments) in certain nerve cells of the eye.
If you are missing just one pigment, you might have trouble telling the difference between red and green. This is the most common type of color blindness. Other times, people have trouble seeing blue-yellow colors. People with blue-yellow color blindness almost always have problems identify reds and greens, too.
sex-linked disorders
allele (which is usually recessive) is found on the 23rd pair of chromosomes (sex chromosomes)… Usually on the X chromosome
Hemophilia, color blindness

37. Chromosomal Abnormalities in Number
What causes an abnormal number of chromosomes?
non-disjunction
failure of paired chromosomes to separate during meiosis 1 or meiosis 2
chromosomal abnormality disorders
result from errors in chromosome # or structure
Down Syndrome (trisomy 21), Klinefelter’s Syndrome (XXY)

38. Disorders Due to Abnormal Chromosome #
What is Down Syndrome (trisomy 21)?
when person has 3 copies of chromosome # 21
What is Klinefelter’s Syndrome?
a sex-chromosome disorder in which males have extra copy of X chromosome
XXY (or 47, XXY b/c 47 total chromosomes)
What causes Down Syndrome (trisomy 21) & Klinefelter’s Syndrome?
non-disjunction
failure of paired chromosomes to separate during meiosis 1 or meiosis 2
Down Syndrome (trisomy 21) = 3 copies of chromosome # 21
Klinefelter’s Syndrome = Scientists believe the XXY condition is one of the most common chromosome abnormalities in humans.  About one of every 500 males has an extra X chromosome, but many don’t have any symptoms.
Klinefelter's syndrome is typically caused by what is called non-disjunction. If a pair of sex chromosomes fails to separate during the formation of an egg (or sperm), this is referred to as non-disjunction. When that egg unites with a normal sperm to form an embryo, that embryo may end up with three copies of the sex chromosomes (XXY) instead of the normal two (XY). The extra chromosome is then copied in every cell of the baby's body.
chromosomal abnormality disorders
result from errors in chromosome # or structure
Down Syndrome (trisomy 21), Klinefelter’s Syndrome (XXY)

39. Chromosomal Abnormalities in Structure
What is causes structural abnormalities in chromosomes?
pieces are added, deleted, inverted, or translocated
chromosomal abnormality disorders
result from errors in chromosome # or structure
Down Syndrome (trisomy 21), Klinefelter’s Syndrome (XXY)

40. Review & Animations Vocab interactive Crosses Drag & drop genetics
Crosses
Drag & drop genetics
Various
Genetic disorders