20 Patterns of Genetic Inheritance

Question 1

Genotype

Answer 1

Symbols for specific gene type (TT or tt)

Question 2

Phenotype

Answer 2

The physcial or outward expression of the genotype.

(How genes make something look)

E=dominant, unattached earlobe

e = recessive, attached earlobe

EE-unattached earlobe

Ee-unattached earlobe

ee-attached earlobe

MUST BE HOMOZYGOUS RECESSIVE (ee) FOR A RECESSIVE TRAIT TO BE SEEN IN PHENOTYPE

Question 3

Alleles

Answer 3

Alternate forms of specific gene at the same locus (chromosome position)

Eg. allele for unattached earlobes or attached lobes.

Alleles are in pairs, one on each of the paired chromosomes - one allele comes from each parent

Gametes (sperm or eggs, being N or haploid) only carry one allele for each characteristic, so if an individual has the genotype Ww the possible gametes this inidividual can form (and therefore traits they can pass on to offspring are either a “W” or a ‘w’ - but not both

Question 4

Dominant Allele

Answer 4

The trait coded for will always be expressed (be seen in the phenotype), and will mask a recessive allele - is usually denoted as the capital letter, eg. “T”.

Question 5

Recessive Allele

Answer 5

Only expressed in the phenotype when a genore has two of this type of allele - is usually denoted as a lower case letter , eg. ‘t’

Question 6

Homozygous dominant genotype

Answer 6

Both alleles of the pair are dominant (TT)

Question 7

Homozygous recessive genotype

Answer 7

Both alleles of the pair are recessive (tt)

Question 8

Heterozygous genotype

Answer 8

one dominant allele and one recessive allele in the pair (Tt)

Question 9

Autosomal Trait or Autosomal Linked

Answer 9

Alternate forms of a specific gene at the same locus (position) on one of the autosomal (body or non sex) chromosomes, numbered 1 through 22

Question 10

Sex Linked Trait

Answer 10

Alternate forms of a specific gene at the same locus on either an X or Y (sex) chromosome

Question 11

Cross

Answer 11

When parents’ trait mix

1. One trait cross - considers the inheritance of one characteristic Eg. WW x Ww
2. Two trait cross - considers the inheritance of two characteristics Eg. WWTT x WwTT

Question 12

Autosomal recessive disorder

Answer 12

• affected children can have unaffected parents
• heterozygotes (Aa) have an unaffected phenotype
• two affected parents will always have affected children
• affected individuals with homozygous unaffected mates will have unaffected children
• close relatives who reproduce are more likely to have affected children
• both males and females are affected with equal frequency

Question 13

Autosomal dominant disorders

Answer 13

• affected children will usually have an affected parent
• heterozygotes (Aa) are affected
• two affected parents can produce an unaffected child
• Two unaffected parents will not have affected children
• both males and females are affected with equal frequency

Question 14

Tay-Sachs Disease

Answer 14

(Autosomal/Recessive)

Seen in central and eastern European Jews - lack of the enzyme that breaks down lipids result sin excessive lysosomes in brain cells and eventually death of a baby, usually by age 5.

Question 15

Cystic Fibrosis

Answer 15

(Autosomal/Recessive)

Seen in any ehtnicity.

Cl- does not pass normally through cell membranes resulting in thick mucus in lungs and other places, often causing infections.

Question 16

Phenylketonuria (PKU)

Answer 16

(Autosomal/Recessive)

Lack of an enzyme needed to metabolize a certain amino acid (phenylalanine). Affects nervous system development - reponds to special diet.

Question 17

Sickle-Cell Disease

Answer 17

(autosomal/receissive)

Mostly sub-Saharan African descent. Red blood cells are sickle shaped rather than biconcave because of abnormal hemoglobin (one amino acid in protein is wrong). Sickle cells clog blood vessels.

Heterozygotes may show sickling with hypoxia (low oxygen) or dehydration.

Question 18

Hunthington disease

Answer 18

(Autosomal/Dominant)

Huntington protein has too many glutamine amino acids, leading to the progressive degeneration of brain cells.

Question 19

Polygenic Inheritance

Answer 19

Two or more pairs of alleles govern one trait

• each dominant allele code for a product, so these effects are additive
• results in a continuous variation of phenotypes
• environmental effects cuase intervening phenotypes
• e.g. skin color ranges from very dark to very light
• e.g. heigh variation

MULTIFACTORIAL TRAIT: a polygenic trait that is particularly influenced by the environment, such as skin color influenced by the sun, or height can be affected by nutrition

Question 20

Environmental influence on Phenotype

Answer 20

• Himalayan rabbit’s coat color infuenced by temperature
• An Allele responsible for melanin production appears to be active only at lower temperatures
• The extremities have a lower temperature and thus the ears, nose, paws and tail are dark in color

Question 21

Incomplete Dominance

Answer 21

When the hetrozygote in intermediate in phenotype between the 2 homozygotes

Eg.

Curly Hair - CC x cc - Straight Hair

         =   Cc - Wavy Hair

Question 22

Multiple Allele Inheritance

Answer 22

• When a gene exists in several allelic forms
• A person can only have 2 of all the different possible alleles (oe on each of their homologous chromosomes)
• A good example is the ABO blood system
• A and B are co-dominant alleles
• The O allele is recessive to both A and B, therefore to have O blood type, you must have two recessive O alleles

Question 23

Co-Dominance

Answer 23

When both alleles are equally expressed in a heterozygote

Type A Blood-AA x BB-Type B Blood

              =          AB

The type AB blood has characterisitc antigens of both blood types A and B on cell surface

Question 24

Sex Linked Inheritance

Answer 24

Traits controlled by genes on sex chromosomes (X and Y)

• X-linked inheritance: the allele is carried on the X Chromosome
• Y-linked inheritance: the allele is carried on the Y Chromosome

MOST SEX-LINKED TRAITS ARE X-LINKED.

Question 25

X-Linked Disorders

Answer 25

• more often found in males than females because recessive alleles are always expressed in males (they only have one X chromosome)
• most X-Linked disorders are recessive

1. COLOR BLINDNESS: most often characterized by red-green color blindness
2. MUSCULAR DYSTROPHY: characterized by wasting of muscles and death by the age 20
3. FRAGILE X SYNDROME: most common cause of inherited mental imperment
4. HEMOPHILIA: Characterized by the absence of particular clotting factors that cause blood to clot very slowly or not at all

Question 26

Human Genome Project

Answer 26

Begun in 1990 and completed in 2003, The
Human Genome Project was an
international effort to determine the sequence
of approximately 3.3 billion base-pairs
(adenine/thymine, guanine/cytosine) which
make up human DNA, and to identify and
map the approximately 20,000–25,000
human genes