Chapter 12

Mutations, Xs, and Inheritance

Mutations= changes in organisms DNA

• Beneficial- lead to adaptations and aid evolution of a species

• Harmful- the worst are lethal

Types of Mutations

1.cellular mutations;a. germ cell mutation-change is in the gametes

so it affects the offspring and not the parent organism

b. somatic cell mutation-change is in an organism’s body cells will affect the organism but not the offspring

ex; certain types of skin cancer, leukemia

Chromosome mutations1. Deletion- loss of part of X so missing

genes and lack info

2. Inversion- one X breaks off a part and attaches in a reverse pattern

3. Translocation- X part breaks off and reattaches to a non-homologous X

4. Nondisjunction- Xs do NOT separate during anaphase of meiosis so one gamete gets too many Xs and gets too few

Gene mutations-

(DNA---mRNA---aa---protein)

point mutation- if only 1 base is affected1. Substitution

2. Insertion

3. Deletion– #2 and #3 cause a change in the codon sequence-

called frameshifts

Ex. THE CAT ATE THE RAT

TTH ECA TAT ETH ERA T

TEC ATA TET HER AT

Genetics Traits

1. Single allele traits;a. Dominant allele Ex- Huntington’s Disease-HH or Hh will develop disorder-hh is normal-genetic marker used to IDb. Recessive allele-Heterozygous will give a carrierEx 1- cystic fibrosisFF- normal Ff- carrierff- normalEx 2- sickle cell anemiaAA- normal Aa- carrieraa- diseased

Genetic researcher Thomas Morgan

• Worked with fruit flies,

Drosophila melanogster• Why fruit flies?

1. chromo. # = 8 (4 pairs)

2. Reproduce quickly

3. Males and females look differentt

• Observations

1. males not like females

2. females had 2 XX and males had 1 X and 1Y

3. called this the sex determining pair

4. other 3 prs. alike in both sexes (autosomes)

5. Had either red or white eyes

Morgan’s experiment with eye color

• Took a male with white eyes and crossed it with a red eyed female.

• Result was that ALL offspring had RED eyes!!!(F1)

• Crossed 2 offspring together and got 3 Red eyed:1 white eyed; however ALL white eyed flies were males this time!!!

• Why did that happen????

The Answer

• Sometimes a gene appears only on the X or Y chromosome

• These genes are called sex linked genes• Ex-Drosophila eye color, 2 possible alleles

red (R) or white (r)• Allele only on the X chromo.• Genotypes= X R X R or X R Xr = red eyed females

XrXr = white eyed femalesXRY = red eyed malesXrY = white eyedmales

Morgan’s 2nd Experiment

• Hypothesized that genes that are inherited together are found on the same chromosome

• Studied body color (GRAY vs. black) and

wing length (LONG vs. short)

• Crossed GGLL x ggll

• What do you think he got???

Answer to GGLL x ggll

• In the F1 all were GgLl (GRAY, LONG wings)

• Morgan then crossed GgLl x GgLl• Results were 3 GRAY, LONG :1 black,

short• Expected 9:3:3:1, instead results are

always 3:1 for two characteristics• So Morgan concluded that these were

“Linked Genes”

Linked Genes

• If known linked genes do NOT follow a predicted pattern they may have crossed over during meiosis

• Ex.- pigmentation of human eye, hair, and skin color• Chromosome maps-• Determine how far apart genes are on a chromosome• Geneticists use frequency• (%) of cross-overs in offspring to determine distance

between genes • called map unit• Rule; for every 1% of crossovers the genes are 1 map

unit apart (p.224)

Chromosome Mapping

• Geneticists use frequency(%) of cross-overs in offspring to determine distance between genes

• called map unit• Rule; for every 1% of

crossovers the genes are 1 map unit apart (p.224)

12-2 Pedigrees

• used to study the inheritance of a trait through many generations

• patterns of phenotypes can be followed using a chart

Genetics Traits

2. X-linked TraitsAllele on X chromosome• 2 needed for female phenotype• 1 allele for male phenotype• Ex- color blindness, hemophilia and Duchenne MD3. Sex Influenced Traits• Phenotype affected by sex hormones• Ex- Baldness • BB is bald in male and female• Bb is bald only when testosterone present• bb- no baldness

Genetic Traits

4. Multiple Allele Traits• Determined by three or more alleles• Ex- ABO blood type• Alleles- A and B (codominant)• O recessive4 Phenotypes : Possible genotypes

Type O OOType A AO, AAType B BO, BBType AB AB

Genetic Traits

• 5. Polygenic Traits

Controlled by 2 or more genes

Ex- melanin amounts

In Hair, skin, eye color

Genotypes- AABBCC- darkest

AaBbCc- lt brown

aabbcc- lightest

Genetic Testing

• Before a fetus is bornA. Amniocentesis- takes sample of amniotic

fluid. - can only be done

week 14-16B. Chorionic villi- taken from chorionic villi

- can only be done week 8-10

• Both require a karyotype be done after cells are samples.

Genetic Diseases and Counseling

• Refer to page 246-247

• http://www.youtube.com/watch?v=goEZ7feoZVk

Gene Therapy

• Gene Therapy – a technique that replaces a defective gene with a healthy gene.

-has been used to treat cystic fibrosis

• 2 types of gene therapy

1. somatic cell- body cells are changed

2. germ cell- changes to egg and sperm