15. in horses, three coat-color patterns are termed cremello (beige), chestnut (brown), and palomino (golden with light mane and tail). if two palomino horses are mated, they produce about 1/4 cremello, 1/4 chestnut, and 1/2 palomino offspring. in contrast, cremello horses and chestnut horses breed true. (in other words, two cremello horses will produce only cremello offspring and two chestnut horses will produce only chestnut offspring.) explain this pattern of inheritance.

To know what happens here, we need to see how alleles work.

You have three species: cremello, chestnut, and palomino all will be homozygotes with two alleles each.  

One of these will be recessive (aa), one will be dominant (AA), and one will be a mixture (Aa).

You know the offsprin, so Cremello and Chestnut are the recessive and dominant ones. If you draw the Punnett square, you'll find out all breeding are pure.

Now, if you draw de Palomino Punnett square having one recessive allele and one dominant allele from each paren, you'll found 1/4 cremello (aa), 1/4 chestnut (AA) and 1/2 palomino (Aa).

blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium of the heart. as the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs where it is oxygenated.