Honors Biology - Ch. 9 Genetics

Trait

Observable characteristic

Alleles

Alternative choices for a gene (they code for the same gene, but one comes from mom and one comes from dad)

Dominant alleles \[hide/are hidden by\] a recessive allele

hide

Recessive alleles \[hide/are hidden by\] a dominant allele

are hidden by

Homozygous organisms have two of \[the same/different\] alleles for a trait

the same (ex. TT or tt)

Heterozygous organisms have two of \[the same/different\] alleles for a trait

different (ex. Tt)

Phenotype

character that is expressed; “way it looks”

Genotype

genetic makeup; “what genes it has”

Generations labelled in punnett squares

P1 (parental) = true breeding parents in genetic cross

F1 (filial) = first filial generation, offspring of the P1

F2 (filial) = second filial generation, offspring of the F1

Mendelian Inheritance

Refers to certain patterns of how traits are passed from parents to offspring. Generally established by Gregor Mendel

Monohybrid crosses

cross to study only ONE character (ex. Aa x Aa)

Law of Segregation

Two alleles separate during gamete formation (separation of homologous partners during Anaphase I)

Dihybrid Cross

Cross to study TWO characters (ex. AaBb x AaBb)

Law of Independent Assortment

Each pair of alleles segregates (separate) independently in meiosis. Maternal and paternal chromosomes mix up in different combinations during gamete formation (Anaphase I)

Result of heterozygous cross (ex. AaBb x AaBb)

9:3:3:1 ratio

For trihybrid crosses or if parents are not heterozygous…

Use multiplication and addition rules to determine ratios and probability of phenotypes

Possible different gamete combinations

2^n, where n= number of chromosome pairs

Testcross

Used to determine if an individual with dominant phenotype is heterozygous or homozygous.

Unknown genotype is crossed with homozygous recessive (A_ x aa)

Non-Mendelian Inheritance 1: Nature vs. Nurture

Environment influences phenotypic expression

(ex. Siamese cats/Himalayan rabbits - darker fur on areas that are cooler. Hydrangea flower color - depends on soil pH)

Non-Mendelian Inheritance 2: Spectrum of Dominance

Incomplete and co-dominance

Incomplete dominance

Heterozygote, blended intermediate phenotype (ex. red x white flowers; heterozygotes = pink)

Co-dominance

Both alleles are expressed at the same time (ex. Roan horse has BOTH white and red hair; AB blood typ)

Sex-linked Genes

X-linked -carried on X chromosome (ex. color blindness; hemophilia; Duchenne muscular Dystrophy)

Multiple Allele Trait

More than 2 choices (A, B, O blood alleles produce A, B, O, or AB blood types)

Polygenic Trait

Trait is determined by more than one gene (ex. skin color, intelligence, eye color)

Pleiotropy

One gene has multiple phenotypic effects (ex. dwarfism, cystic fibrosis)

Glycoproteins

On the surface of blood cells, determine blood type

True/false: It is important for doctors to know a person’s blood when performing a transfusion or transplant.

True

I^A and I^B are \[recessive/codominant\]

codominant

ii (type O) is \[recessive/codominant\] to A or B

recessive

Universal Donor

Type O

Universal Recipient

Type AB

Genetic Screening & Counseling

\-Based on Mendelian genetics and probability rules

\-Tests for identifying carriers

\-Fetal testing

\-Newborn screening

Carrier

Heterozygous individual that doesn’t show trait, but can pass it on to offspring

Pedigree

Diagram that shows how traits are passed over generations

In a pedigree…

Female =

Male =

Individual with trait =

Carrier =

Female = circle

Male = square

Individual with trait = filled in

Carrier = half-shaded

Karyotype

Organizes picture of an individual’s chromosomes

Karyotypes can show…

Sex: XX = female, XY = male

Some Genetic Disorders: missing/extra chromosomes (Down Syndrome, Turner Syndrome, Klinefelter Syndrome), large translocations/deletions (Fragile X)

Karyotypes cannot show…

Gene mutations (ex. PKU, sickle cell)

Amniocentesis

A test that takes a sample of the amniotic fluid by sticking a needle into the abdomen and does biochemcial tests on it. This can’t be done until 14-16 weeks and the whole process can take weeks. There is a risk of miscarriage if you go through this testing.

Chorionic Villus Sampling (CVS)

A testing during pregnancy that can be done once you are 8-10 weeks pregnant. Suction tube is is inserted through the cervix and biochemical tests/karyotyping can be done on fetal cells immediately. There are faster results than amniocentesis, but there is a greater chance of miscarriage than in amniocentesis